I want to sign up for Snapchat and when I put my normal e-mail account, they said my e-mail is associated with a username.
If you receive that message when registering, it means someone or you already created an account on Snapchat. You can get information about the account that's already tied to the account using the Password Reset function. Access the URL below and enter your email. The system will send the password for the account using your email and then you can log-in to see what's with the username.
Password Reset: https://accounts.snapchat.com/accounts/password_reset_request