A Preset is just a set of keywords with a unique name. You can create these sets via Edit -> Presets menu.
As you can see on the picture above, it’s dead simple. Preset “Mountains” has 9 keywords and it belongs to the group “Nature”. That’s all.
To create preset you just click “Add new” and fill in what is needed:
And what you can do with preset is to insert it into keywords in a number of ways.
From the context menu
You can do it from the context menu “Insert preset” of the keywords field.
From the keyword
If the keyword “looks like” the name of existing preset, you can “expand” it to preset. Better see the example.
From the autocompletion
Covered in a separate topic.