When processing a transaction from the Catalog, be sure the user has an account (if needed). To create an account, see Create an account.
If the user already has an account, simply click on and type in the users first or last name.
To find the activity you can use the search and filters on the left side. You can also click on the tabs to find the appropriate item the customer is registering for. Then add items to the cart. Check out or close and add any additional items.