Mr. @Raj1978 use the search bar before creating new threads. Face unlock is a 4-5 year old unlocking method in android but no body seemed to care about it unless it came with the new iPhone.
Face unlock is already included in your system if you tried to search you might have easily found it but ranting on a company forums is always easier than search isn't it, nevermind.
Here is how to activate face unlock
Go to Settings>security and location>smart lock>trusted faces