Visit an event's page (eg, via Calendar link above)
During registration window, there'll be a registration form visible below the event information, usually with an accompanying "how to register" video. If you work at a large multinational corporation, it's possible they will have Air Table blocked, in which case your phone or waiting until you are at home is a work-around.
Fill out the form, which involves hopping over to PayPal to make a payment, and then pasting that receipt number into the registration.
If you miss the preregistration window, there's same day walkup registration, but to reduce waste, maps may be scarce, so pre registering is best (also helps us plan snacks and makes check in faster, etc.)
Per "start", which is your group whether that's you or you and some friends:
Pre reg: $7/member, $12/non member
Same day (maps not guaranteed!): $10/member, $15/non member $5 maps
Additional maps if you want your teammates to backside drive or co-drive: $5 (add that to cart) Pre-Registration.
SI timing stick rental is free, but if you lose the stick, there's a $40 replacement cost. We recommend using the leash or keeping good track of it.
For example, you and three friends are non members, and want to try out orienteering by taking two maps for Yellow, and you've pre registered: $12+$5 = $17 total cost for all four.