how can i make a background image like this?

Hello, its easy for apply a background image (whatever you want) using CSS codes.

For example the website you have provided used the same process to display that background on their website. Let me show you:

Visit the website ciplex.com and view the source code (ctrl+u) and you will see the HTML codes for the website. Look on line 11, there is a link like this "/css/style.css" click on it and you will be into Style CSS file of the website. The background image code is written here. Look for the class "body" (should be around line 22), here is the code:

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body { text-align:center; font-family: Arial, Verdana, Helvetica, sans-serif; font-size:12px; color:#999999; background:#000000 url(../images/bg-body.jpg) no-repeat center top; }
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Now can you recognize the background image URL they have mentioned here?

hope you have understood. Thank you.

that's now what i asked.
i know how to add a background image with css

i am asking about how to design my own image.

because i don't want to use my own image
and not an image stolen from another website.

It is very easy to get that effect in photoshop. They are just lines with a couple filters on them. They are usually called abstract lines or glowing lines/beams etc.

Here are a couple of good round ups of tutorials to teach you this effect in Photoshop which you can d/l a free trial if you don't have it. Some of these might even have the .psd you can d/l at the end of it.

40 Cool Abstract and Background Photoshop Tutorials

30 Best Photoshop Abstract Effect Tutorials

thanks for the links.
i don't have photoshop
but i will try to apply the instructions in GIMP.

Use a pen tool in GIMP, then mess around with colors by changing opacity and outer glow. Gimp let's you do most that Photoshop will let you do. It's not that hard, but I'm not a big fan of spending hours figuring that out.

You may even find a royalty free texture you could use from like sxc.hu, or somewhere else. Investigate, you may not have to create one.

It's easy if you are using PS
pen tool > set the brush settings > stroke the path and add some masks or gradients.
Hope this helps

It's called abstract wallpaper ... You can make in photoshope and also get help from photoshope tutorials..

or you can search for vector graphics