If you make the subgroups first you can then select them and add the subgroups to a new group which will be parent.

You can also add a group to another by first selecting the group you want to add, them click the gear wheel on the group you want to add to and select Add from the menu.

Here's a video a made with some guides how to use groups.

[youtube]kwZtI59Nwkk[/youtube]

Okay! Thank you! And that was an extremely helpful video!

Thank you, I'm glad I could help! 😃

I need help I am on mobile and can’t get it to work is there a button to press to select more than one brick to put in a group?

It's called Selection Tools, the "mouse arrow" button... top button on the left-hand toolbar. It's keyboard shortcut W if you ever switch to a PC. When you click it you'll get a menu of selection options... best way to learn these is to read the label, poke the button and give it a try. Cheers!