Diagnosis
You've got ignition clicks but no fire. The most common culprit is a dead or dying AA battery in the electronic igniter module. That clicking is the spark generator working, but without enough juice, the spark is too weak to jump the gap at the electrode.
How to Fix It
Pop open the battery compartment on the front control panel—it's usually a little plastic door. Swap out the single AA battery for a fresh one. Make sure the battery's positive end is facing the correct direction (the diagram's inside the compartment). After replacing, try lighting again with the lid open so any built-up gas can dissipate.
If That Didn't Work
If you still get clicks but no flame, the electrode tip at the burner might be corroded or misaligned. Find the small metal rod near the first burner. Make sure its ceramic base isn't cracked and that the tip is about 1/8 inch from the burner port. Clean any gunk off it with a bit of sandpaper or a wire brush.
Heads Up
Always open the lid before attempting to light the grill. If gas has accumulated, lighting with the lid closed can cause a dangerous flare-up. If you smell gas but get no ignition, turn the knobs off and wait five minutes before trying again.