The Passcode can be 1 of 2 things:
1. A 4 digit number
2. A more complex string of characters.
The Keyboard to enter the passcode on an iPad will be a 10 digit keypad for the short simple passcode, or a full keyboard for the longer more complex version.
It is set only to access ther iPad and is unrelated to your Apple ID password.
If you can't remember what passcode you set, then your only recourse is to reset the iPad.
iOS: Forgotten passcode or device disabled after entering wrong passcode