https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...
From there, you have a better background for reading the documentation of shell implementations, like Bash.
Also study Awk:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/a...
Those who don't know Awk do comical things with cockamamie combinations of cut, sed, grep, echo ... and clumsy loops written in shell.
Other than shell syntax and semantics, it's a matter of knowing a large number of utilities.