I know about unix/linux processes, ipc and the relevant system calls (exec*, fork, clone, ...) but where do I continue from there? Studying C, I haven't really

I know about unix/linux processes, ipc and the relevant system calls (exec*, fork, clone, ...) but where do I continue from there? Studying C, I haven't really come across threads other than trying out the things in `pthread.h`. Would you recommend just reading the source code of that header for a better understanding?