Enter 5 wrong passwords or pattern in quick succession and you will be locked out for 30 seconds. During the countdown there should be a button at the bottom saying "Forgot Pattern?" or perhaps "Forgot Password?" Select that and it will ask you for the Google account information you used to set up/enroll the device. Enter that email address and password and it will take you to the password reset function for the tablet.
If that doesn't work, your best solution is to perform a factory reset. The technique for doing this usually involves something like pressing and holding the Power button and the Volume Up and Volume Down buttons at the same time. If your tablet has a physical Home button then the method is to press and hold the Power, Volume Up, and Home buttons all at the same time.
For either of these methods, you should soon see the Green Droid or the recovery screen. If you see the Droid, press one of the volume buttons until you see Recovery Mode and then press the Power button to display the Recovery screen. Press the Volume Down button until the Factory Reset option is highlit and then press the Power button again to select it.