mac's keyboard write letters like v and c when I make copy or past, how can I fix this problem?

Sounds like your Command key isn't working. Try using the other Command key. If both Command keys have the same issue, then perhaps a keyboard or accessibility setting has been changed, or if this only occurs within one app, then it is due to a setting within that app.

Try using an external keyboard.

Try booting into Safe Mode to see if you still have the same issue.

Create a new user account. Log into the new user account to see if the issue still exists.