Firstly go to TEAMS & EVENTS > ALL EVENTS and using the FILTER button you can filter by event type, for example Clubs, if you choose you can do a more in-depth search by using the dates or the name of the event.
Once you have found your chosen event click on the event name, this will take you to the event / activity page.
Please note, to mark attendance for a club you will need to have activated it first, please see more information on this in the relevant guides.