In the System settings, under the Logbook tab, you can configure custom settings.

Available are the settings of the tags.

A number of tags have already been predefined. You cannot change the name, color, or description of these tags, nor can you delete the tags themselves. You can tell this by the lock icon in the Actions column.

To add a new tag, click <+ Add> in the header. A new row will open where you can enter a name and description and select a color.