There are two types of features that can be attached to a vehicle in the inventory. The standard features and the special features.
In order to add special features, the user can select a feature from the available in the list by clicking on the checkbox.
In order to remove a special feature a user can un-select it by clicking on the checkbox
The standard features cannot be altered or deleted 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