How to unlock an iphone if you have locked it?

Help!

Press the button that slide in the direction of the arrow shown!

If you mean you've just pressed the lock button. Press the button at the top of the phone then slide where it says slide to unlock.
If you are locked out and that won't work… Plug your iPhone in to the computer and restore it using iTunes. (Google it if you don't know how!)
Hope this helps

If the iPhone is currently disabled due to locking it too many times, you will have to do a restore in iTunes, meaning your data, etc will be erased.