← Reading the Manual (man pages)
Find a command by what it does
Learn
Finding a command you don't know the name of
Sometimes the problem is the opposite: you know what you want to do but not which
command does it. apropos (equivalently man -k) searches the one-line summaries of
every manual on the system for a keyword:
apropos "compress"
# gunzip (1) - compress or expand files
# gzexe (1) - compress executable files in place
# gzip (1) - compress or expand files
# ...
Each result is a command name, its manual section in brackets, and its summary. It's the index at the back of the book: search by topic, get the command names back. Put the phrase in quotes when it's more than one word.
Your task
Now the reverse: you don't know a command's name, only that you need to "list directory contents". Search every manual's summary by keyword with apropos (the same as man -k).