I want to have a black background and know how to do transparent too. And to put a image as background.

Thanks

Inkscape default background color is transparent, although it is shown as white. You can change it in Document Properties (Shift + Ctrl + D), click on the Background box to get a pop-up where you can change the color.

You can import a bitmap image into Inkscape document using the Import option. Use Pixelsnap extension on the image so it doesn't get blurred and if you like you can lock the layer with the image so it doesn't get moved accidentally and do all other work on another layer.