Help rebooting system that was mistakenly erased

I tried to do a restart holding the R button but unfortunately, I do not have a backup drive. I thought I did but it turns out it’s the back up drive for my older computer that has El Capitan on it so that does not help me. I need to update the system, but it was my father‘s computer that he gave to me and he forgot his password so the App Store won’t let me upgrade to the latest version. I tried to wipe it clean to start over and now it does turn on, but I can’t seem to get it to do anything else. I just get the usual window with the options. I can get on the internet, but because I don’t have the latest version of Safari, the browser is out of date and it won’t let me do anything.

I was hoping to make an appointment and bring it into the genius bar unless somebody has a better idea.

thanks