Thanks. Once they are then back in a wallet then the private key comes into play again?
More correctly, once you get the coins from Coinfloor into your Electrum wallet... then your Electrum seed phrase comes into play.
If you have those 12 words, you'll be able to recreate your entire Electrum wallet. That is to say, any and all private keys that it generates from that seed phrase. Those 12 words are all you require. Make sure you have them securely and safely backed up offline.
Do not store a screenshot of them, do not store them unencrypted in digital form on an online computer or cloud backup service etc.