Where can I find the guide and the code to start Atomic Swap?

You can get the code and Atomic Swap launch guide at https://github.com/minexcoin/atomicswap

NOTE: Keep in mind, atomic swap currently runs on testnet of each cryptocurrency you exchange.

Testnet is a network where you only use test coins. Test coins are aimed at testing some features or functions. Test coins do not have market value.

Mainnet - is the main network, where the coins with market value are operating.