You work in a team. You are working on feature 1. I am working on defect 1 and 2. And our tech lead is working on an integration POC. It is possible there will be three branches - feature, defect and integration and of course the master.
We each checkout our code into our respective branches.
We build and test using Jenkins on our own branches. Now you complete your delivery, you will raise a PR to merge the code with the master. The reviewer reviews and confirms the PR.
Now imagine from feature branch you have 3 branches - 3 people working on a single feature. Or maybe from the feature branch - you have 3 sub-branches for each developer. Once you check-in you raise a PR to merge to feature branch. Build and testing done on the feature branch.
It really depends on how your org and team are managing the branching system.