How do you make Back grounds like that? i mean really i want to know how to make a background like that

Its easy really,

from what I can see its only gradients and C4Ds, which I must say blended well and added well to the flow and lighting

To begin graphics design you must take many, many tutorials/practices/etc.

1. Download and many example sigs as you can.
2. Download as many C4Ds/stocks as you can.
3. Sign up to a gfx website such as sigresouce and gfxheaven there you can ask for help and view tuts.

To make that BG you could
1. Create a gradient similar to the overall color scheme (light blue :3)
2. Light source - make a new layer, and then get a white brush, make it 60 and make a dot. Smudge it out to your liking.
3. Add colored C4ds.
4. Done.

c4ds are make by cinema(tic or whatever) 4d. You can find tuts/examples on google.