For the verb "to be" in the present tense:
* est (for the third person singular, meaning "he/she/it is")
* suis (for the first person singular, meaning "I am")
* es (for the second person singular, meaning "you are" [formal or informal])
* sommes (for the first person plural, meaning "we are")
* êtes (for the second person plural, meaning "you are" [formal or informal] or the third person plural, meaning "they are")
For a question, you can use:
* est-ce que (before the verb)
* est-il (for the third person singular, meaning "is he?")
* est-elle (for the third person singular, meaning "is she?")
* est-ce (before a noun or pronoun, meaning "is it?")
Examples:
* Elle est belle. (She is beautiful.)
* Je suis fatigué. (I am tired.)
* Est-ce que tu es prêt? (Are you ready?)
* Est-il malade? (Is he sick?)
* Est-ce un chat? (Is it a cat?)
Remember that the conjugation of the verb "être" (to be) changes depending on the subject pronoun and tense.