The biggest difference between a tablet and a laptop is portability. A tablet can be slipped into a bag (or if you have a smaller 7" screen tablet, a jacket pocket - just) without you being weighed down.
Laptop computers however typically come with far more storage than a tablet. You can pick up a cheap laptop (or notebook) computer with 500Gb of storage, whereas the average tablet has between 16Gb and 128Gb of storage.
Tablets are largely designed to consume content (reading books and magazines, watching films and tv shows, browsing the Internet), whereas laptops are much better suited to content creation.
On price, tablets range from £129 to £450, whereas laptop cost more, but you get more features, and laptops are far more configurable.