Adding field to signup

Hi, I was wondering how troublesome it would be to add a field to the sign up form? I tried searching for the obvious queries related to this, but came up empty-handed so excuse me if I am asking a dumb question.

I tried looking at the signup page to add in a field to display the user’s name but it looks really packed full of stuff so I’d rather just not touch it until I have a better idea of what I’m doing..