Is there a way to give someone access to the gui shop, without putting it into console command everytime a new person joins? Like in startup parameters or something?

Grant the permission guishop.use to the default group.
https://umod.org/documentation/plugins/permissions

So do we need to put people in a group or how does that work?

By default, you have two groups, admin and default. The default group is automatically for everyone. Now, if you want all your players to be able to use the shop, grant permission to the default group.

oxide.grant group default guishop.use

So where do I put that under? Like what file? Or does that just go under the console command?

It's a console command

Sadly that did not work. Typed it into console command, and nobody had any permissions.