IMHO, the first step would be to learn how to use Linux (if that's not done). For that, just install some Linux distro and use it. Maybe start with Ubuntu, and try to use the command line as much as possible (instead of using the graphical user interface).
When you feel comfortable with Ubuntu, maybe try Arch Linux. You will learn a lot just by installing and configuring Arch (but you will be lost if you have no experience of Linux, hence something like Ubuntu first). Arch Linux has a very good documentation!
When you feel comfortable with Arch, try compiling packages manually. With the Arch AUR you can do that pretty easily (get a PKGBUILD and build the package). Again, that's all documented by Arch Linux!
When you feel comfortable building packages manually, maybe it's time to try Linux from Scratch: https://www.linuxfromscratch.org/. It will go one step further than the way you installed Arch Linux, and this time you will compile all the packages manually!
At this point you will have learned a lot and it will be easier to see how to move more into the kernel.
Note that this is just my opinion: maybe you can get into the Linux kernel without understanding how the Linux OSes work, but... well that's not how I would do it :-).
Comments
IMHO, the first step would be to learn how to use Linux (if that's not done). For that, just install some Linux distro and use it. Maybe start with Ubuntu, and try to use the command line as much as possible (instead of using the graphical user interface).
When you feel comfortable with Ubuntu, maybe try Arch Linux. You will learn a lot just by installing and configuring Arch (but you will be lost if you have no experience of Linux, hence something like Ubuntu first). Arch Linux has a very good documentation!
When you feel comfortable with Arch, try compiling packages manually. With the Arch AUR you can do that pretty easily (get a PKGBUILD and build the package). Again, that's all documented by Arch Linux!
When you feel comfortable building packages manually, maybe it's time to try Linux from Scratch: https://www.linuxfromscratch.org/. It will go one step further than the way you installed Arch Linux, and this time you will compile all the packages manually!
At this point you will have learned a lot and it will be easier to see how to move more into the kernel.
Note that this is just my opinion: maybe you can get into the Linux kernel without understanding how the Linux OSes work, but... well that's not how I would do it :-).