They help you specify what your users can and can't do on their account as part of the company.
The roles and permissions allow you to differentiate between roles such as sales reps and managers. You can then have your managers/admins do things that your sales reps wouldn't have access to.
To adjust permissions for a given role, go to Roles on the left-side menu, then select the role you want to update the permissions for. Once you've made your changes, click Save. This will be updated in real-time.