Here is a short list of the man pages I found most helpful in this course (check out the manExamples.py script in this directory to find more of them for yourself!):
getopt
man 3 getopt
man 3 string
shared memory
man 3 shm_open
man 7 sem_overview
man 7 shm_overview
fork, pipe, execle
man 2 pipe - also has fork
man 2 dup2
man 2 wait
man 3 system
socket
man 2 select_tut - also has sigaction
man 7 unix - has overview
man 3 getaddrinfo - fallback, if no ipv4 given