Модальные глаголы can, could, should, have to, must

The verb “Can”.

После модальных глаголов не ставят частичку to.
I can help

Глагол не спрягается.

I can
You can
He can
She can
It can
We can
They can
You can

Could-Мог бы?

Could you please join the chat?
Could you please call me