"flashing light" is a timing light. If you look down at your timing chain cover from the drivers side, you should see some notches with numbers next to them. 0 would represent Top dead center or TDC), everything after that is Before TDC.
I believe the auto stores will loan you a timing light. so here are the steps to take
clean up them marks so you can see what you are aiming at. there is also a notch on the balancer (big disc right in front of the timing chain cover) try to get a little white paint in that notch so you can see it easier (or chalk or whatever will make it stand out) you might need to bump the ignition a few times to where the notch is visible to get to. of course this is all done without the jeep running.....
now once they are all cleaned up, start the jeep and let it warm up to operating temp. there is a bolt on a hold down clamp on the distributor. it is under the distributor, on the motor, on the front facing side. mine takes a 1/2 inch wrench. loosen that bolt up so the distributor can be rotated, but still tight enough that is doesnt move on its own. hook up your timing light to the battery and the 3rd clamp to the #1 spark plug. disconnect the vacuum advance line off of the distributor and plug it. if youre a golfer, a golf tee works perfectly. I suppose even if you dont golf, a golf tee will still work LOL. now move your light over to the side where the notches are and point the light at those notches. you should see the mark from the balancer line up with one of the numbers on the marks on the timing chain cover. this is your current timing. if you need to adjust it, slowly turn the distributor to set the timing. try not to use the cap to turn the distributor, I cant remember exactly which direction does what, but one way retards the timing while the other side advances it. you will notice when you move it that the idle speed changes a bit. if you hear the motor start to knock or ping, go the opposite direction until you achieve a good running idle. a good starting point is 8*. set it to 8*, tighten the clamp, and hook back up the vacuum advance line and drive around and "feel" how the jeep runs. try to notice ant flat spots or hesitations or listen for any pinging or knocking in the motor. after that if you need to, repeat the steps and adjust the timing until you feel the jeep runs smooth in low and high RPMs. Hope this helps out, and if you have any questions feel free to PM me. Im always willing to help good luck!