First step which goes for creating anything in blender is to... OPEN BLENDER!!! :)
Second, right click on the lamp to select it and then press "x" to delete it. Then go to the 2nd layer.
Then add an icosphere to the scene.
After that, duplicate the sphere by holding down shift and pressing "d". Continue to duplicate until you have 6 total spheres. Then switch to cycles render engine.
Next, add a different emission shader to each sphere, but make them all pure white. Then for each sphere, change the strength value. Make the values of the different spheres: "5" "2.5" "1" "0.5" "0.25" "0.1"
Then select all the spheres and press "CTRL G" to create a group, and name it stars.
After that, go back to the first layer and create a particle system for the cube.
Set the number to "2500: and the start and end at "1". Also select volume.
After that, select group and pick the group you created. Uncheck emitter, and then check "Pick Random" and set the size to "0.002" and Random Size to "1".
Next, go to top view and shrink the cube along the y-axis to make it the same as in the picture to the side.
Now go to front view and position the camera so that it is just inside the edges of the first face of the cube.
Go to the world settings and change the background color to black.
Now render out the image and save it by pressing "F3".
BONUS: CONTINUE IF YOU WANT TO ADD SOME COLOR VARIATION
If you want to add some color variation to the stars, add a new scene.
Then go to the 2nd layer and add 6 icospheres again. Give each one a shadeless material with a different color.
Select all the spheres and make it another group called Colors.
Then go back to the 1st layer and add a plane. Next create a particle system for it. set the number to "50" and the start and end to "1".
Now go to the render tab and select the group you just created. Check "Pick Random" and set the size to "0.5".
Now add a camera and position it above the plane like the picture to the side. Then render it.
Now go to the compositor and make it full screen. Check use nodes and backdrop. Then press "CTRL + Shift + Right click on the render layers node".
After that, add a blur node, change it to fast gaussian, and set it to 20x20. Then add a HSV node and set the saturation to 0.75. Next add a multiply node. Then add the image of the stars created earlier, and blur it like previously, but 1x1 and select "x". Plug this node into the bottom of the multiply node. Then add an add node and plug the multiply node into it. Then blur the original star image again by 0.25x0.25 and plug this into the bottom of the add node. Then make sure it is connected to the composite node.