There are exceptions, for example être starts differently (so you can't use nous sommes) but the endings are all the same. The stem for être is ét-:
Note that the endings for the imperfect tense are always the same.
Verbs like manger add an extra -e before -a, -o, -u. You take it from nous mangeons and it becomes:
With verbs like commencer, the last -c becomes -ç before -a, -o, -u. Nous commençons - BUT NOT in the nous and vous forms: