What do I need to be able to craft ammunition in this game?

Loading bench (there is one right in Goodsprings next to store) and ingredients. Just click bench and you can see what you need for each round. However you can not make rounds just from material scavenged around wasteland. In order to make some ammo, you probably need to brake down another one. So its more like changing one type of ammo to another you need ...and not just any ammo. Click bench and you will see.

I'll be honest with you, I've never crafted any ammunition in the game and I played on hardcoe, and I went guns and repair to 100.

Also what is 'Drained Flamer Fuel' and do i want it?
Its the same with breaking down ammo, I don't know what it means to 'breakdown' :S

Drained flamer fuel can be recycled at work benches if you have enough of it.
For the ammo crafting, you need to be at a reloading bench. You have options to craft or breakdown ammo. Crafting turns components into ammo, breaking ammo down turns ammo into components. To make ammo, you need lead, shells, or cases or hulls(whatever they're called) of the correct ammo type, and some powder that matches the type(pistol, heavy pistol, rifle, etc.)

I'm not convinced that crafting adds much beyond masses of inventory clutter, but appreciate this may be different on harder difficulty settings. I don't feel guilty about ignoring it for now though.

I actually use it often, I use the lever action shotgun and I convert all my regular rounds into slug rounds, it's also helpful if you can find ingredients for ammo that's hard to find in stores.