The first step to using Den is signing in. Instead of web2 authentication, Den uses Sign In With Ethereum.
In the Sign In With Ethereum model, Den provides a message for you to sign with your wallet. By signing this message, Den is able to verify that you are the true owner of the wallet. Signing this message does not enable any assets to be transferred or otherwise affected.
An example message is shown below. You can read more about Sign In With Ethereum here.