How to setup Approvals within Quick Base

Depends on the complexity of your approval flow. If it's fairly simple you can do it with form rules primarily - where you have your 'approval' fields on whatever form you're working with and only certain assigned users can access it or sign off and then you log the person that did it and the timestamp it occurred. 

If you have a more complex workflow I prefer to do it more like a template based approach where each approval is it's own record in an 'Approvals' table. This could be based on a master table of approvals that you reference when someone submits, or you can just blanket create the same approvers each time. In either case - each record is it's own approval assigned to someone. 

I typically prefer the latter route - it gives you a lot more flexibility downstream when/if the process gets more complicated, but if you just need a simple solution and the people aren't dynamic or overly complex then the simple/field based approvals will work.