I know this sounds like a dumb question but, me and my friend wanted to work on a game at the same time.
Not sure what you mean but Unity doesn’t have any collaborative editing features built-in. However if you use source control then multiple people can work on a game at once.
At the same time like the both of you making changes in real time (like GoogleDocs colaboration)? Unity is not prepared for that.
You can use any remote access software and control your firend’s PC from your PC, but there’s only one cursor and you’ll end up “fighting” to control the mouse or focusing a window. Teamviewer has a free version, you can try that, but there are lots of options for that.