How do i change a picture of mine into a microsoft theme? Do i have to save it as a certain file type or what?
If your using Windows 8/8.1 you can set the picture as your desktop background by locating it in your file explorer, right clicking it and selecting set as background. If you want to set the picture as a tile or the lock screen you need to open said picture In Windows picture viewer and select Set AS option at the bottom of the screen.
Once done you can save your "Theme" by right clicking on your desktop and selecting "Personalize". There you will see the option to save your theme as well as other options for setting back ground, colors, sounds, and screen savers.