Some general hints to help you learn:
1) in a terminal, use the apropos command to help find commands: appropos group
would give you a list of all commands on your system having anything to do with group.
is your friend and largest resource for information on Linux-related issues.
3) the LQ forum has a search function. Use it frequently. Most problems you encounter have probably already been asked.
4) include in your post which distro you are using. The command-line tools will probably be the same for most, if not all, distros. But, each distro may have it's own set of GUI tools. Knowing the distro you use helps others with experience with that distro to give you helpful directions.