The Waves Platform uses a seed to access your account. The seed can comprise several random words (presently 15 if using the wallet seed generator) - although if you type a seed in manually you can change this and add non dictionary words/symbols if you like.

The seed is cryptographically highly secure and you need to write it down and store in a safe place. Do not ever divulge your seed to anyone, for any reason. Do not keep your seed on an insecure location. I use veracrypt to store mine off-line. https://www.veracrypt.fr/en/Downloads.html

The seed is all you need to access and use your wallet - 2FA solutions are coming for other applications and it's possible many users will use these as well - but for users, the seed is what you need for now.

You cannot change the seed and use the same main and additional addresses. For example; If you have the slightest suspician your seed may have been compromised you should create a new seed, take note of the new Waves address and transfer all your Waves and tokens to the new address.

Download the client and try it out for yourself. https://wavesplatform.com/