To Be

In English, the verb "to be" can be used to tell how something is (the condition) and what something is (the essence).

How is the apple?
It is unripe.

What color is the apple?
It is green.

In Spanish, a different verb is used to express "to be" depending on whether the speaker intends to address a condition or an essential quality.

La manzana está verde.
The apple is green. (condition)

La manzana es verde.
The apple is green. (essence)

Note how the adjective "verde" actually changes meaning, depending upon whether it is used with ser or estar.

La manzana está verde.
(condition: verde = unripe)

La manzana es verde.
(essential characteristic: verde = color green)

To address condition, use estar. Estar is an irregular verb. It does not follow the standard rules of conjugation for regular -ar verbs. Therefore, you must memorize it.

estar

estoy
estás
está
estamos
estáis
están

To address an essential quality, use ser. Ser is also irregular and must be memorized.

ser

soy
eres
es
somos
sois
son

If you are talking about what something is, use ser; if you are talking about how something is, use estar.

What is she like?
She is quiet.
Use ser:
Ella es callada.

How is she acting?
She is being quiet.
Use estar:
Ella está callada.

http://www.studyspanish.com/lessons/serest1.htm
http://www.studyspanish.com/verbs/lessons/piserestar.htm

Demonstratives

"este" (sans accent) est l'adjectif démonstratif: cet, cette, ce...-ci, cette...-ci.

exemples:

 este teléfono: ce téléphone-ci esta lámpara: cette lampe-ci 

"éste" (avec accent) est le pronom démonstratif: celui-ci, celle-ci

exemples:

¿Por qué éste?

Indefinite Adjectives

Here are the most common indefinite adjectives along with their common translations and sample sentences:

• algún, alguna, algunos, algunas — some, a few, any — Algún día voy a España. Some day, I'm going to Spain. Tiene algunos libros. He has some books.
• cada — each, every — Cada día voy a la oficina. I go to the office every day. Tenemos un libro por cada tres estudiantes. We have one book for every three students. (Cada is invariable, making no changes with number or gender.)

• cierto, cierta, ciertos, ciertas — certain, specific — Quiero comprar cierto libro. I want to buy a certain book. Ciertas estudiantes fueron a la biblioteca. Certain students went to the library. (This adjective is not preceded by un or una. When used after a noun, the word means "true" or "accurate.")
• cualquier, cualquiera — any, whatever, whichever, whoever, whomever — Cualquier estudiante puede aprobar el examen. Any student can pass the test. Estudia a cualquier hora. He studies at whatever time. Podemos viajar a una ciudad cualquiera. We can travel to any old city. (A plural form, cualesquiera (both masculine and feminine) exists but is seldom used. When cualquiera(masculine or feminine) is used after the noun, it emphasizes that the specific identity of the noun is unimportant, somewhat like "any old" in English.) Note that through apocopation, cualquiera is shortened to cualquier when it comes before a noun.
• ningún, ninguna — no, not any — No quiero ningún libro. I don't want any books. Ninguna mujer puede salir. No woman can leave. (As in the first example, a double negative" can be required in Spanish when this adjective is used before the object of a verb. The plural forms, ningunos andningunas, exist but are seldom used, even though an English plural form is used in translation.)
• otro, otra, otros, otras — another, other — Quiero otro lápiz. I want another pencil. Otra persona lo haría. Another person would do it. Quiero comprar los otros libros. I want to buy the other books. (This adjective is not preceded by un or una.)

• todo, toda, todos, todas — each, every, all, all of — Todo estudiante conoce al señor Smith.Every student knows Mr. Smith. Corrieron a toda velocidad. They ran at full speed. Todos los estudiantes conocen al señor Smith. All of the students know Mr. Smith. Durmió toda la noche.She slept all night. (When it means "each" or "every," todo/toda is used in singular form before the noun. When it means "all of," the adjective precedes the entire noun phrase, as in the examples.
• varios, varias — several — Compró varios libros. She bought several books. Hay varias soluciones. There are several solutions. (In singular form and sometimes in the plural form, the adjective also can mean "varied," "different" or "various.")

Note that while some of these adjectives can be translated as "any," the English word "any" is often left untranslated into Spanish: ¿Tienen ustedes libros? Do you have any books? No tenemos libros. We don't have any books.

http://spanish.about.com/od/adjectives/a/indef_adjective.htm

NINGÚN, ALGÚN, CUALQUIER

Cualquier=masculine (cualquier hombre=any man)
Cualquiera=feminine (cualquiera mujer=any woman)

I guess when you can replace "any" with "some" leaving the meaning intact, then you translate it as "alguno/a", otherwise, it's "cualquier-a". Ejemplos:
"Any suggestions?" (here, the meaning would be almost the same if you replace "any" with "some" -some suggestions?- so you translate it as "alguna"): "¿Alguna sugerencia?" (you can also say "¿Cualquiera sugerencia?")

On the other hand, "any man could do it" wouldn't mean the same if you replace "any" with "some" ("some man could do it" doesn't mean the same as the original phrase so you say "cualquier"): "Cualquier hombre puede hacerlo" (here it doesn't mean exactly the same if you say "alguno hombre puede hacerlo")

http://forum.wordreference.com/threads/cualquier-vs-alguno.662761/

cualquiera - pronoun: anybody, anyone. / adj.: any, whatever; whichever

alguno - pronoun: some, any / adv.: a few / . adj.: some, any; not ... any; one

Most of the times they are not interchangeable.

http://www.spanishdict.com/answers/154361/cualquier-vs.-algunoalguna


Ninguno/a (none, no) shortens to ningún before a masculine, singular noun. When it follows the verb, a double negative is required:

No hay ningún problema. ¿Tenéis amigos? No tenemos ninguno. Ninguna sociedad es perfecta.

There is no problem. Do you have any friends?We have none. No society is perfect.

Ninguno/a is never used with plural nouns (with some unimportant exceptions):

No tienen ningún pariente = No tienen parientes. No hay ninguna dificultad = No hay dificultades.

They have no relatives. There are no difficulties.

Alguno/a (some, any) shortens to algún before a masculine, singular noun, and varies in gender and number according to the noun it refers to: alguno, alguna, algunos, algunas:

¿Hay algún museo en la ciudad? Necesito un taxi. ¿Ve Ud. alguno? Algunas sociedades son muy estrictas.

Is there any museum in the city? I need a taxi. Do you see any? Some societies are very strict.

Cualquiera (any at all) shortens to cualquier before any noun, and normally occurs in the singular:

Llámenme si hay cualquier problema. Necesito un taxi. ¡Cualquiera! Cualquier sociedad tiene gobierno.

Call me if there are any problems. I need a taxi. Any one at all! Any society has some government.

https://www.bowdoin.edu/~eyepes/newgr/indef2.htm

Words that contain "-gun-"

ningún/ninguno/ningua = any (negative)

algun/alguno/alguna = any/some

algunos/algunas = some

segundo/segunda = second

según = according to

pregunta = question

preguntar = to ask

To be or not to be masculine

Here is a list of nouns that should be one gender but be another.

El guardia/la guardia

el artista/la artista

Preterite (Past) Conjugation Patterns

For -ar verbs, drop -ar and add:
é
aste
ó
amos
asteis
aron

For -er and -ir verbs, drop its ending and add:
í
iste
ió
imos
isteis
ieron