Q: I don't remember how to log in in my mackbook

Yes, it you set it up that way.

You can reset the password using these instructions if the Mac has Lion or later and yo do not use File Vault:

https://www.macobserver.com/tmo/article/os-x-mavericks-how-to-easily-reset-ther- administrator-password

How long have you not logged in?  Is the data there important?
If not, why not reset it?