SSH connection to gitlab allows gitlab ssh servers to access my computer?

I know i can create a ssh key and access gitlab server but that means my computer can be accessed by gitlab too? someone shared a private project with me and i want to know if that person or gitlab can put data in my pc too

No, ssh access is one way. You would have to explicitly configure things to allow someone to log in to your computer.

But project is not mine, just this other person gave me access, this person could configure these things to access my computer or i just can do it from my computer to allow that access? And gitlab could access my computer i guess as allows pulls, so can update my local project

No, this does not give anyone access to your computer.

If doesnt give access then how pulls are made?