|The bar the Start button is on is called the Taskbar. |
Most people like to have the Taskbar at the bottom of the screen, but it can be at the top of the screen, or at either side.
RIGHT click on a blank part of the Taskbar.
If Lock Taskbar has a checkmark before it, click on the Lock Taskbar to remove it.
(There will be no checkmark beside it the next time you look there.)
Hold your cursor over the Taskbar, hold down the left button, and drag the whole bar to the bottom of the screen, let go of the left button.
If you don't want the Taskbar to move, then RIGHT click on a blank part of the Taskbar, click on the Lock Taskbar and it will be enabled (there will be a checkmark beside it the next time you look there).