Website login certificate?

Question

Digital certificates

I'm trying to learn the certificates for entering the site.
They talked about the fact that there is such a thing as special "files" when opened, the user on the hardware on which this file was opened has permission to enter the site (in his personal account, for example)
I don’t know how to explain this, but maybe someone knows that I I mean, where can I read about it?
like a profile or something