Personally, I think 'Learn by screwing-up' is the most permanent way to learn anything. Just ALWAYS be aware of the prop arc and stay at least twice as clear as you THINK you need to be.

Please tell us what type of engine you have and what you have tried.

I will assume it is a small 2 stroke like a .40 or .46.

There are three things which must be present simultaneously for the thing to fire, compression, fuel and spark (heat). I often had trouble starting early on because I had too little fuel in the engine to start with. Put your finger over the carb and turn the prop (WITHOUT THE GLOW IGNITER CONNECTED TO THE PLUG), until there are no bubbles in the fuel line and there is a VERY slight increase in resistance. Then (USING A CHICKEN-STICK), and with the glow igniter connected, turn the prop in either direction with one smooth stroke. Your stick and all nine (just kidding) of your fingers should be far away from the prop arc at the end of the stroke. If the engine begins running backward, blip the throttle a bit and re-start if it dies. Often it will run correctly even if you start it backward. I usually start mine backward, I don't really know why.

Hope this helps. AND No, you will not damage your engine by starting it backward.

HINT: If air is rushing toward the tail, it's running correctly forward. (This is not meant to be a joke).

Tuning is usually covered in the manual, but there is an art to it. Just keep working with it and your instructor will tell you when it's right. There should be a smooth transition through the throttle and at full throttle, there should be a slight amount of visible smoke.

Good Luck!!