|I'll walk you through it...|
First, you should right-click (or secondary-click, whatever floats your boat) your taskbar and look for "Lock the taskbar", making sure that is it unchecked.
Next, you should simply be able to 'drag' it down to the bottom of your screen. To do this, left-click (or primary-click) an empty space on the taskbar and keep the button held. Continuing to hold the left button down, move your mouse and cursor down towards the bottom of the screen. The taskbar --or "Start Button", as you called it -- should 'snap' into place; once that has happened, simply release the left button.
Finally, if you want to keep it there and prevent it from being accidentally moved again, you should right-click on the taskbar once more and make sure that "Lock the taskbar" IS checked.
Alternatively, you could right-click your taskbar and click on "Properties". A screen should pop up, called "Taskbar Properties". Make sure that the "Taskbar" tab is selected and look four lines down to where it says "Taskbar location on screen". To the right of it there should be a drop-down menu. Click on the menu and select "Bottom" then click on "OK" at the very bottom of the window.
And that concludes my most pointless essay of the month.