Today I spent time learning the forms of ”to be”. I watched this video
Interestingly you almost always drop the present form есть in real life (video has more about it).
I picked following three singular perfective forms of ”to be” or ”olla” as my daily words:
Masculine (я/ты/он ) бы́л
feminine (я/ты/она́) была́
neuter (оно́) бы́ло