Nothing is easier than that.
Go to the events tab and click the New event button.
Fill in the details about the event, then add the event to your existing event portfolio.
If you'd like to customise your event fields, here is an article that explains it pretty well.
Link member activity to this event
💡 Did you know that with every import of members via .csv, we automatically tag members with a specific timestamp?
We will use this functionality to link members to an event. Follow me >>>💡It's important to upload separate event-related .csv lists according to the activity they've performed.
The following loom explains it pretty well
If there is anything you would like to change or need help with, please contact your success manager, and in case you don't have one yet, please drop us an email at firstname.lastname@example.org