A fan forced oven keeps the whole oven at an even temp whereas a non fan forced one has different temperature zones from top being hottest, middle then bottom being coolest. That's pretty much the difference.

My oven is fan forced but I find it oven cooks way too slow when I put it on the fan forced temp the recipe suggests so I always go with the normal temp.

You'll get used to it after you use it a few times. The best way to gauge how your oven cooks is to make a few cakes.