What does logging in to your D Link router do?

Question

oh and how can I reset it to default and will it cause problems?

Answer 1

Logging into your router allows you to set up the features of your router.  If its wireless it allows you to set passwords and encryption.  It also lets you set a password and special features for gaming.  If you reset it to factory defaults you lose all settings you might have in there now and the password gets reset to the default.