The verbs in French are much more complicated to conjugate than in English. They change according to the subject, and the tense and modes are more numerous.

Être (to be) is among the most complicated because you cannot see the common radical.

• I am = je suis
• You are (singular) = tu es
• He is = il est
• We are = nous sommes
• You are (plural/polite form) = vous êtes
• They are = ils sont

Sites like leconjugueur gives you all the forms of a verb according to person, time and tense. Here is the example for être, for instance.

When at school, I commonly used the Bescherelle, which is still a reference book for conjugation.