есть is the verb "to eat", есть being the infinitive. быть is the verb "to be", with есть being the present tense form of the verb, which can roughly be translated are "there is". It is somewhat of a special case as usually only the past and present tenses are used with this verb.

есть = TO eat, есть = am, are, is etc. (But _usually_ есть translates 'have': 'I have a...'='у меня есть... ' or 'there is/are' ) быть = to be

* it sounds :)

Он есть мужчина - it's sounds like foreigner is trying to speak Russian.

Он есть мужчина means he is a man; он ест мужчину means he eats a man. =)