What must I do before kick-off?

Under Law 6 your pre-match duties are:

• The toss: one captain tosses a coin and the other calls. The winner decides whether to kick off or to choose an end. If the winner chooses an end, the opponents must kick off, and vice versa.
• Clothing and studs: the match officials must inspect players' clothing and studs for conformity to Law 4.
• Front rows: the match officials must check the availability and status of front-row players under Law 3.10 and the scrum engagement process in Law 19. Each team must tell you its front-row players, possible front-row replacements and the positions each can play.

If no referee has been appointed, the two teams agree on one, and if they cannot agree the home team appoints a referee.