Gunpowder is a fairly easy to craft resource in Ark. It is mainly used for ammo, flare guns, and most things that go BOOM! Producing it in smaller quantities can be quite easy, though for larger quantities the right tools and a little finess go a long way.
To create Gunpowder you'll need a Mortar & Pestle. Once you have that you'll need a good load of Charcoal and Sparkpowder. It takes 1 Charcoal and 1 Sparkpowder to make 1 Gunpowder.
Now you'll need a lot of Gunpowder to make ammo and explosives. And I mean a lot. Luckily, you can use more than 1 Mortar & Pestle at a time, so doing a few batches doesn't have to be too painful.
As far as making a ton of Charcoal and Sparkpowder, that doesn't have to be too painful either. For tips and tricks on bulk production and resource collection, please see:
Charcoal & Bulk Production
Sparkpowder & Bulk Production