You can use the man utility to view information regarding config files and programs. For instance lets say we wanted to learn more about the sshd_config file.
The above command would then output information regarding that configuration file, and how you can go about configuring that file.
You could also look up information on how to use various utilities such as useradd.
The above command would output information as well as the various flags available to the useradd utility.
Lets say you werent sure what the name of the command was. You could also search through the man pages using a keyword. Using the -k flag will search through the short descriptions as well as the names for each of the man pages.
man -k search_term
The info utility allows you to read the info documents for a given utility. The info can sometimes be useful if you did not find your answer using the man pages.
The above command will open the info pages for the passwd utility.
You can also search through the info pages using the -k flag as such.
info -k passwd
The utility apropos allows you to search the manual page names and descriptions as well. Each manual page has a short description available. To use apropos do the following.
The above command will output any manual pages that contain ssh in either the name or short description.
Reading the documents in /usr/share/doc
If for some reason you cannot find information regarding a particular program in the man or info pages. Then odds are you’ll have a directory full of info at /usr/share/doc. You can navigate that folder to find the information you need and read the files using the less pager or cat.