How to unstick my light switch?
The switch was probably damaged by a short circuit caused by wiring your fixture incorrectly.

So - how do you fix?

Step 1:  Turn off the fuse/breaker that was blown/tripped when you caused the short

Step 2:  Remove the face plate for the broken switch

Step 3:  Remove the screws that anchor the switch in the electrical box.  Do not remove any wires.

Step 4:  Study the switch and make careful note of where each wire connects.  The old switch should have markings on it that indicate things like "hot", "neutral" and "ground".  Take some sticky labels like mailing labels and write down each connection on a label and stick that label on the wire before you remove it from the switch.

Step 5:  After you've labelled all the wires and removed the switch, take it to your local hardware store and buy a replacement.

Step 6:  Come home and reconnect the wires exactly as they were before.

Step 7:  Mount the switch in the box.  Replace the face plate.  Turn on the power in the fuse/breaker box.