First you insert a text box from the Insert menu.
You click and drag a text box from left to right and press as many Enters as there is necessary to reach till the end of the bottom row on the slide.

To have it filled in a certain color, simpy press with your right mouse button on the text box and choose Format Shape. From the Fill menu choose the one suitable for you and note that you can also choose the color of your liking.

Hope this helps.


Rgrds,
Kristiina