Hooks generally come in two types; barbed & Barbless. Most fisheries require you to use barbless hooks.
For course fishing you will use anything from a size 6 to a size 20 (the bigger the number the smaller the hook). A size 6 would be for very big baits like 20mm boilies and a size 20 hook would be ok for a single maggot.
Always match your hook size to the bait you use and the weight of the hook to the type of fish you want to catch; a strong gauge hook would be needed for carp for example.
There are also 2 ways to attach them to the line, some have a spade end (for which I’d recommend buying a hook tying tool) and others have an eye which can be tied using various knots, take a look at the useful knots page.
If you