Your account on assignr.com is created by your assignor. Once your account has been created, you will receive an automated email
Just click the link in the email to get started. The assignr.com site will display your login name, and you'll be asked to provide a new password for your account.
The login screen will allow you to login with either your email address or your user name. If your email address is associated with multiple assignr.com accounts, you will need to use your user name (your email address won't work to login).