How to track the source tree of kernel

Hi Guys, Sorry to bother you all. I'm just starting learning linux with a rpi4b. I found the raspi source tree have many branches, which are different from the kernel source tree, which also have many branches. I want to know how should I track the source code. should I track all branches from the remote repo, or just stick to a specific branch? How did you do so that you can catch up to lastest kernel? Thanks in advance! Sincerely, A Linux newbies.