If you have Android 4.x or lower, go to all apps on the homepage (the dots ) click on widgets, find the Google search bar, long press it, put it where you want it to be.
If you have Android 5.x or higher, swipe your fingers from two opposite corners (for example: upper right, and down left) to the middle, click on widgets, find Google search bar, long press it, put it where you want it to be.