You can read more about the verb 'to be' and its conjugation here : http://grammar.ccc.commnet.edu/grammar/to_be.htm

Verb to be have three forms in the Present Simple Tence (am, is, are). They means "be" (be clever - I am clever - He(She, It) clever - We(They, You) are clever). In this tence forms are used to describe anything or anybody. To do an action you have to use "do". But in the Present Continuous Tence verb "to be" is used with the other verbs (I am working). You can write me message and I tell you about "to be" more ;))