NOTE: In order to invite users to events based on custom user attribute values, the attribute must be a single or multi-select attribute.

Custom user attributes are a great way to track additional user data, as well as sort by that data. Some common examples of custom user attributes are homeroom teacher, student ID, t-shirt size, and clubs/organizations.

How to set up custom user attributes:

Dashboard -> Settings -> User Attributes -- from this screen you can set up text attributes or drop-down attributes. Users can fill in/select the values whenever they login next, or the values can be imported via .csv file.

Support resource: Importing user attributes.