When you want to create a new role, to set different permissions for the users, you can do that by going to menu / settings / permissions and click on the pink "+" button.
Then you just have to select a name for the role and save it. It is now listed in the overview. When you want to edit the name of an existing role, you can do that by clicking on the three little dots next to the role.
Now you can click on the role an set the permissions. You will find more about how to manage the permissions here.
You can easily change the role of a user. First you have to click on the arrow on the right side of that role. Then you can see all the users who are in this role. After that you just have to drag and drop the user in a different role. Now the user got all the permission of this role.