When you select a permission preset, the permissions are applied from the preset, and get displayed in the matrix - but you cannot click the matrix and change them, unless you switch to the Custom... - then, the preset values are shown in the editable matrix and you can change them.
The presets simplify the granting of permissions.
Every object has different presets.
If you are unsure if the preset is suitable for your purpose, use the manual permissions on the matrix instead.
About the standard presets
Note: the explanation of the standard presets is made on the example of a folder. Have in mind that it works for every 'container': folder (containing articles, images, videos etc), typography (containing formats, fonts, styles), titles (containing editions, pages etc), and similar. See Which items inherit permissions? for further info.
•View: allows only to view the content of the folder. You cannot do any editing. You cannot send or delete items in the folder.
•Read: allows only to view the content of the folder and crop referenced images. You cannot do any editing. You cannot send or delete items in the folder.
•Send to: includes Read and also allows to send content in the folder, but you cannot send from that folder.
•Edit in: includes Send to and also allows to send content from the folder, to assign and remove the referenced content (e.g. multimedia to articles, or assigning articles to editions).
•Change in: includes Edit in, and also allows to place/send for all classes of content in the folder, but not yet to edit content.
•Change: includes Change In and also allows editing of content of all classes except Protected, and does not include deleting of content.
•Full Control: includes all permissions.
•None: no permission.
•Custom: you can select the permissions in the matrix. If you select Custom, after already applied a preset, it keeps the preset values, so you can modify them. Note: in that case, you're not modifying the preset itself, but the values copied from the preset.
Adding new presets
Since version 2.2, the presets are configurable, in the PermissionsSets.xml in the Global subfolder of Config. Therefore, you can set your own presets by modifying the file and reloading it in the database.
In the versions prior to 2.2, the presets are hard-coded.