How do you start a rugby union game?

With a drop kick.

--

A team kicks off with a drop kick which must be taken at or behind the centre of the half way line.

If the ball is kicked off by the wrong type of kick, or from the incorrect place, the opposing team has two choices:

To have the ball kicked off again, or

To have a scrum at the centre of the half way line and they throw in the ball.