That's Parental Controls enabled.
If you're under 18 and your parents enabled it, check with them to see if they can disable it or give a permission
If your parents haven't enabled it, someone else did it (if you bought used, probably the old owner had it enabled). If you don't know the pin and no one put that restriction for you,
you should call Nintendo or email them. Check at support.nintendo.com.
You can also bypass the PIN using a tool Neimod created (not recommended if you/your parents/someone close know the PIN) :
http://gbatemp.net/threads/parental-control-h4cked.340642/
Tip: Using Caps Lock, "PLZ" and other internet stuff won't help you much on GBATemp