Welcome to Bestmind(TM)!
Try to guess the hidden four-digits combination.
The answer will be a certain number of "1" and "0".
The "1"s stand for a right digit in the right position.
The "0"s stand for a right digit in the wrong position.
For example, if the hidden combination is "3865" you'll get:
1234 --> 0
3567 --> 100
3856 --> 1100
3865 --> 1111