Gathering allows your character to get items used to create new items of various types.
To gather you will need the appropriate tool with the exception of foraging- which you can do without the aide of a tool. You usually gain plants, herbs and other small hand held items from foraging, it differs based on your area.
Gives you one of 3 types of wood. Oak, mahogany and ??. Axe needed, axes can be crafted out of iron or purchased from Boss.
Will give you a random fish- fishing pole needed. Fishing rods can be crafted out of iron or purchased from Thornton.
Mining will give you ores, mostly iron and occasionally Eludium. You need a hammer to mine, which can be purchased from Boss or crafted with forging skill.