Yeah...study always helps before “jumping in”, basically like FReeper Palmer said above, you can derive your private key from CoinBase, but you DON’T want to use that CoinBase private key to transfer the funds to an “intermediary” wallet before you record your seed words in steel. CoinBase could use that key to drain your Bitcoin later if they wanted to...you need a new private key and TRANSFER/SEND your Bitcoin to the new fresh/unadulterated by an exchange BTC wallet address/private key. So: from exchange/CoinBase-—>send BTC-—>to new never used BTC wallet/private key-—>record seed words from the new trusted/fresh wallet-—>stamp seed words/phrase into steel-—>delete “intermediary wallet”-—>put seed words/phrase in a safe place.
There are advantages to seed phrases and using a hardware wallet and most apps you have no choice. However Mycellium allows an exception, you can simply scan a private key and t will store it in phone memory (encrypted and as secure as the seed phrase).
If you think Mycellium is not good for any reason, please let us know.