Go to Guest List. You can create and add 'Tags' to any guests. To create a Tag, click on the Tag+ icon > Add New and create your desired tag.
To apply this tag to any guest(s), select the checkbox to the left of their row in the Guest List, then click Tag + icon > [name of tag].
You can filter the Guest List to display guests by the Tags assigned to them. Click on the Tags icon to open up the Tag Filter modal.
Note: If you select more than one tag to filter by, the result will be any guests who are assigned all the selected tags