Open Preset opens up a file open dialog where you can select an existing Preset.
Once a Preset has been selected the Open Preset window will appear.
Click Open to close all open inputs and replace them with this Preset.
Any settings included with the Preset will also be applied (See here for more information)
Click Append to add the inputs in this Preset to the existing session.
Any settings included with the Preset will be ignored.
Each input can be unticked if you want to exclude it from being added
Quickly open a recent preset by clicking the arrow button next to the Open button.