In order to add features the user can select a feature from the available in the list by clicking on the checkbox
In order to remove a feature a user can un-select it by clicking on the checkbox
The standard features cannot be un-selected since they are inherited from the model tree.
In order to save any changes the user selects 
button.
To add or remove features is controlled by a business case that the user must have in his role.
More information on how to add or remove features can be found in this page: → Add Feature