Paint? As in Paint XP standard on any Windows? That's my bread and butter Hallo!
First, I'm not sure what your question is, but I'll give the basic solution:
If you're trying to paste a single figure onto another background, make sure that everything around the figure is *one solid color.* Then select the figure with the select tool(I forget the exact symbol, I think it's a dotted line), either hit "control 'C'" on your keyboard to then copy the selected figure, or right lock it and select "copy" from the pop-up window. Then, open your desired background with another window, and either hit "control 'V'" on the keyboard, or right click and select "paste." ("control 'P'," the more logical combination, prints your picture, which isn't what you want right now.) when the figure appears on the background, hit the bottom on the tool bar that has the three shapes, each transparent, which will make every pixel of your selected background color transparent. You may need to change the background color on this new window(represented by the second color box, lower left hand corner) by right licking on the appropriate color in your color palet. If your background is a custom color, use the color picker tool to select the custom color(be sure to right click it). You will have to undo your paste, however, "control 'Z'," and then repaste it, but it should work.
Like I said, I wasn't sure of the question, but I hope this helps!