You can go back to where you bought your device or to a professional but that will cost money; the ones I'm showing you are free.
Step 1: Use your google account
At the bottom right part of the screen, you'll see "Forgot Pattern" button. Tap it and it will ask you to enter your email and password. After you entered those fields, tap "sign in" and you'll go to google play. There you'll see instructions. Just follow them and you'll be ok.
Step 2: Boot to Android System Recovery
You can start by powering off your device in any way you can.
Removing the sd is optional.(If you remove them, the apps you have on your sd card will still be there but it won't be installed so it wastes memory.)
Then turn it on while pressing volume down button.