Answer:
If you are invited to an after-party, respond as you would to any party invitiation. If you are invited to Temple for the actual ceremony , and wish to go, RSVP in the affirmative , show up a few minutes early , ask for a yarmulke if you are a male guest , and allow yourself to be seated wherever the usher wishes to seat you. Same for female guests minus the yarmulke, Bring a headscarf if not sure of what the particular Temple requires of females. Just stand and sit as the congregation does, and follow along as best you can.