You will get idea in this tutorial how to draw simple background with stars and nebula. Simple and effective for backgrounds.

Step 1.

In photoshop open up a new image sized 350×350 px, and fill it with black color.

Step 2.

Create a new layer, choose a Brush tool and make a few white dots, here and there, different sizes, like on the photo below. (Name that layer “stars”)
New layer with white stars

Step 3.

Now double click on your “stars” layer, check only “Outer Glow” checkbox and enter the settings for glow, like on the picture below.
Outer glow

Step 4.

Create a new layer (name it “clouds”). Change your foreground color to this: #bff8ff, then change your background color to this: #002040.

Step 5.

Now go to Filter -> Render -> Clouds. Change a blending mode for layer “clouds” to Hard Light. like on the picture below.
Blending mode

Step 6.

Now your got something like this:
Current result

Step 6.

Change now your foreground color to #eaff5b. Create a new layer on top of Background layer. Use your Brush tool and fill some spaces with that color, like we did below:
Green nebula

Step 7.

Next, go to Filter -> Blur -> Gaussian Blur -> for radius enter 54 pixels. Click on OK. Then change the blending mode for that layer you just painted, from normal to “Pin Light” and you are done.


Final result