Touch and hold the home screen (any empty space where you can see no app) and select widgets option. From there select the clock you like anolog or digital. Done
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By the way lockscreen is the screen  you first see when you press the power button and swipe to unlock almost like the screen you see on windows where you enter your password. Touch phones give the option of either swiping your phone to unlock or add a password or number pin option to secure your phone. Check these out in the settings>security
And homescreen is like your windows desktop.[/QUOTE