A barb is a type of hook that is designed for things to get caught on. Barbs are found on barbed wire, some fish hooks, some arrows, some plant seeds and some animals have barbed claws or teeth. A hook that is barbed is usually very difficult to get out of whatever it is stuck into. Barbed seeds are bad for animals, as they can get stuck in the animal's skin or inside their mouths and are very hard to get out, so can cause bad infections.
Garb is a word that describes either a style of clothing, or the clothes you are currently wearing. The girl in the picture is wearing renaissance garb.