Liberal Gun Owners

Ok, so I just bought my first shotgun (former military, and longtime pistol/rifle owner). I've got next to zero experience with shotguns however. It's a GForce GFY-1 i bought it without reading reviews, which say it jams a lot. Whoops. Anyways, it comes with 3 chokes, and I have no idea which is for what scenario. Can someone ELI5 the use for them?

Also after reading reviews it says you can't use slugs, why is that? Also, if I can't use slugs, is it ok to use other spicy ammo like dragons breath or flechettes or anything?