Q: How do I used the iPhone with id and password is not my

You can't if iOS 7 is installed. Only the previous owner can unlock it for you.

Find My iPhone Activation Lock- Removing a device from a previous owner's account

If you cannot find the previous owner, then you now own a paper weight.

Paperweight = Unusable.

The previous owner must either give you the login credentials or remove the iPad from their iCloud account.

Have a nice day.

If you purchased it used, return it if you can.

Hopefully you used paypal or a credit card so you can get your money back.

No.   That will do nothing.

Tell him he has to login to iCloud and delete the iPhone from his account

This is the web address... He should type into browser.

https://www.icloud.com/ipad_welcome/