Past and cancelled events do not take an RSVP
The button is replaced by a cancelled tag once an event is called off, and an event that has already happened refuses the RSVP. Guests can only be added while the event is still ahead of you.
RSVP is one button. It tells the organizer to expect you, puts your face on the event page, and unlocks the guest counter and the calendar file.
Open the event
From the events list, or from a link someone shared with you. You have to be signed in: a visitor sees who is coming but gets no button.
Press Add me
The green button in the RSVP row. Your avatar appears in the list underneath straight away.
Add the people you are bringing
Your own tile in the attendee list grows a plus and a minus. Each press of plus adds one guest and the tile shows the running count.
Put it in your calendar
Add to calendar downloads this one event as a file your calendar app understands.