A user role is a way of limiting down how your account users use your account, by default ever new user on your account is considered an "admin". If you wish to limit a user to only be able to do certain things, then a new user role can be created. User roles can be created via your account page.

And the permissions of those roles can be edited via the cog provided next to the role name. You will then be given  a list of permissions you can apply to that role. Simply click the permissions you wish to apply to that role and save.