Smart contracts, mate, they're a bit like vending machines. You put something in (like Bitcoin), the machine runs the code and automatically spits out what you bought (like a soda).

They're self-executing contracts with the terms of agreement directly written into code. They can be used for all sorts of things - from simple transfers to complicated decentralized applications.

As for cryptography, smart contracts use similar principles as Bitcoin itself. It's all about secure and verifiable transactions on the blockchain.

But remember, while Bitcoin does support basic scripts and multi-signature transactions, if you want full-fledged smart contract functionality right now, you'll have to look at platforms like Ethereum that were built specifically with this in mind!