There are many ways to take screenshots. In distros like Ubuntu, Mint or Fedora, the tool is either gnome-screenshot or mate-screenshot. You can also use more complicated tools like shutter or GIMP. They are good at what they do. But I myself always want to take screenshots quickly and silently , thats why scrot – a command line tool – is always my favorite.
Scrot is most likely not pre-installed in all distros but installing scrot is easy since it is available in every repository. You hence just need to open the terminal and type the basic installing command to install scrot.