if the battery and battery conections are good, then you need to replace the starter motor
It will probably be your starter motor Starter is out!
sounds like the starter solenoid, you will have to replace the starter
Try and turn the Impreza engine over by hand. The engine could be locked up and not let the starter turn it over.
The starter is located just behind the top end of the engine. I have a '99 king quad. Mine solenoid clicks too. I thought it was a loose wire because sometimes it would turn over but I took it in and was told i need a new stARter. they run about $75.
Basics, If the battery is OK and the starter just clicks it is the starter. If the starter turns the engine over but won't start it could be a crankshaft or camshaft sensor or fuel pump. It needs to be diagnosed or it can be extremely costly to just replace a lot of unnecessary parts in it.
Replace the starter motor
One of a few things depending on the click. If it makes consecutive clicks when you turn the key (click,click,click,click) then the odds are the battery is dead or in need of charging and there just isn't enough charge to fully engage the starter and turn over the engine. If it clicks just once, the selenoid is usually bad, or the starter is "locked" and will need to be replaced.
broken tooth on the fly wheel if your starter is turning over and not just spining what's wrong if the starter's just spinning?
If you hear the starter spinning but not turnover it over. Or if the starter just clicks when you try to turn it over. If anything you can just take it out and have your local auto parts store test it.
bad connection or starter solenoid
I would check your charging system. If you turn over your key and your starter just clicks, it is usually a low battery charge or your starter is out. I would suggest jumping off your vehicle and taking it to autozone and have them do a charging test for free.
When and if the engine stops at the point where the starter gear is aligned with the missing teeth the starter will just spin and not start the engine. Over time even if the starter turns the engine over it will eventually ruin the starter. You need to replace the flywheel and the starter immediately.