Depends on when you are doing this. The following are the instructions for a "Hard Reset", which totally wipes the device. If you are trying to save data on it, then you would do better to go into the tablets settings and try the reset that is in there.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together...