This is the 413th most frequent Russian word.
начать
To begin; to start.
In this sentence, 'начал' is the past tense of 'начать,' indicating that the action of starting happened in the past.
Он начал работать в новой компании.
He started working at a new company.
Here, 'начинаем' is the present tense of 'начать,' showing an ongoing process of starting to do something.
Мы начинаем изучать новый язык.
We are beginning to learn a new language.
Here, 'начать' is used as an infinitive verb, meaning 'to start.' It depicts the action of initiating something.