Can any one please explain to me when should I use está in place of es?
As far as my understanding goes es translates to is and está translates to this.
But sometimes I see that está is translated as is, too.
There are two verbs representing English to be: ser and estar.
Es and está are conjugated forms of ser and estar, respectively. Precisely, it's the third person singular. Está is also the spelling for second person (tú) in imperative mood (cf RAE).
The difference of these verbs is discussed a lot in every beginner book and in hundreds of tutorials on the Internet; for instance on about.com.
There are also a lot of question on that topic on this site. Search for "ser estar" or browse through the cópula tag.
That said, ésta (with the accent in the beginning) is also the spelling for the singular feminine demonstrative pronoun representing this.
It just happens to be like that. But there's no confusion because the demonstrative pronoun represents a noun (or–when used as an adjective–it precedes a noun) and the conjugated verb form is part of the predicate.
As an adjective: Esta mujer está loca. This woman is crazy.
As a demonstrative pronoun: Ésta está loca. This one is crazy.
"es" (verbo ser) is pretty much forever, part of the object.
Él es ingeniero.
"está" (verbo estar) is temporary.
Juan está en África. El Cairo es en África.
I can think of very few cases in which you have to decide which one to use:
Él es enfermo de SIDA. Él está enfermo, con un resfriado.
Lex Luthor es un científico loco. ¡Cómo? ¿Estás loco?
La pared de la casa es roja. Mi cara está roja de la vergüenza.
Jorge es calvo. ¿Viste a Jorge? Está casi completamente calvo.
Marte es un planeta muy frío. El agua para cocinar ya está caliente.