Testnet is a second bitcoin network that works like the real one, except its coins have no value. Developers use it to test software; we use it to teach (sample guide).
In our workshop you set up a wallet in testnet mode, write the recovery words on paper, wipe the wallet and restore it. Then you send a test payment to your neighbour and watch it confirm.
Practising on testnet first means the first real mistake you avoid is the expensive one. Holding your own keys means nobody can reverse a mistake or recover lost words for you.