You could be a little more specific, i.e posting some code to show what you have to get more specific answers. Anyway, you can draw a bitmap on top of another bitmap by using something like this:
//You will have a Bitmap bottomBmp, a Bitmap topBmp and a Canvas canvas.
//If you are inside an onDraw() method the canvas will be provided to you, otherwise you will have to create it yourself, use a mutable bitmap of the same size as the bottomBmp.
canvas.drawBitmap(bottomBmp, 0, 0, null); //Draw the bottom bitmap in the upper left corner of the canvas without any special paint effects.
canvas.drawBitmap(topBmp, 0, 0, null); //Draw the top bitmap over the bottom bitmap, change the zeroes to offset this bitmap.