I assume you mean the verb conjugation of the present perfect? It's used to talk about things that started in the past, but are still going on right now (in the present) or something that happened recently.
To form it use the past participle of haber + the past participle of another word. For example:
He visto las montañas de Perú
(I have seen the mountains of Peru)
Hemos vuelto para comprar la leche
(We have returned to buy milk)
Habéis cantado muy bien
(You have/You've sung very well)
If you need more info, here is a good place: http://www.spanishdict.com/guide/spanish-present-perfect-indicative
First estas has to have an accent it needs to be estás
I think that is it
C. Because sea is being used with respect . Since you are talking to someone older than you!
