Step 1: First click on Rectangle tool 
and
make a shape look like this:
Step 2: Then click on Custom Shape:
Step 3: And make some star in this shape look like this one:
Step 4: then click on Filter/Render/Lighting Effects in these option:
Step 5: Then see these options:
Step 6: Then see these options:
Step 7: At last your Background is finished:
