Unlock iPhone

iPhone 4 isn't on iOS 10, so slide across the screen with your finger left to right where It says slide to unlock, then enter you password. If your talking about a device on iOS 10 or later, press the home button then enter your password.

Push the home button and enter the four digit (or longer) code.

IIt did not work it says my passcode has zero values

You will need to contact your wireless carrier and first see if they are willing to unlock your device. If they are, they will usually send you an email which will contain the passcode to unlock the device.

I forgot my code to unlock my iphone

See here: https://support.apple.com/en-us/HT204306

One way to do this is to connect the iPhone to your PC or Mac that has iTunes downloaded and fully updated.
It will then unlock the iPhone but also do a factory reset for security and privacy issues.

IF you can't press the home button until there is an apple logo showing up

Go to find my iphone and erase it.

If the screen is blank, hold down the on buton untill the apple logo shws up then stop holding it down. When the screen has the lock screen displayed on it, repeat what I said above

Press home button and switch off button together at once.