Check existing user and group in linux for beginner

I've been checking through the internet to find out a simple command to find out I have what group in my Linux, Fedora:

getent group

so it'll display all the available group with user in return.

to simple return current user's group, simply use:

groups or groups <username>

to display a user's group.

User link to refer: 

Linux: Show The Groups a User Is In
UNIX / Linux Command To Check Existing Groups and Users