Patching SQL Server 2016

Most of my SQL Servers are on 2016 SP2. The security group have identified that I need a later security update applied and as SP2 is out of support this year I planned to just patch it up to SP3. The problem is I have never actually patched SQL Server and was wondering what a good process would be to follow when applying the service pack. I have seen some online, all roughly the same, but just need some opinions on the best way to go about it. Some questions I have, from looking at these processes online are: - I'm assuming the SQL Server instance will need to be restarted. Is this done automatically when installing the patch? - Does all activity on the instance need to be stopped? I.e., do all application services communicating with the instance need to be shut down? - Should the SQL Agent be stopped as well?