as far as i know the pronounciation of est is "eh" the s and t are silent but for some reason i sometimes hear the t pronounced, in what cases the the t is pronounced ?
French has a phenomenon called liason, where if a word ends with a normally silent consonant and is followed by another word that starts with a vowel, the normally silent consonant is pronounced at the beginning of the next word. For example, c’est un homme would be pronounced as “say tu nom”. Another example: les enfants is pronounced something like “lay zahfah”.
You'll want to read about 'liaisons':
That's what's known as a liaison. When a consonant at the end of a word is followed by a vowel (or an h muet) it usually attaches itself to the next word. For example, "petit ami" (literally "little friend," a slightly old-fashioned way of saying "boyfriend") is pronounced like "pe-ti t'a-mee." Note that there are certain liaisons that are forbidden or optional, and that certain letters change sound when in a liaison. Bon apprentissage ! Happy learning!