There are a number of ways to score points in rugby.  These are:

Try (5 points)
Grounding the ball over the try line.

Conversion (2 points)
Kicking the goal over the goal posts if a try has been scored.

Field Goal (3 points)
A drop kick over the goal posts when in the field of play.

Penalty (3 points)
Kicking the ball over the goal posts when a penalty has been awarded following an infringement.