Akhtaru,
Although this is a fairly straight forward task to do, I think you do need some experience of web design to fully appreciate the ins and outs of skins for DNN. I'm not sure how much you know, so I'll quickly outline my angle on this and then give you options to explore.
As I'm sure you're aware, the panes are where the content of your site goes, and these panes, in most cases, define the available areas within the template, and also control the width of the module content that's placed within them. So when you place a module into the pane, it makes sense that it should be touching the edges of the pane, as it's making full use of the available space.
So when it comes to defining the width of a module, you really have 2 options.
1. Re-define the pane structure to better suit the layout you're after - with div and CSS based skins this should be changable within the skin.css or skinname.css file.
2. Target the module/container in question and alter the width, margin, padding of this. As long as the skin has an XHTML doctype you should be able to set the width of the modules wrapping element, and by setting the margin to "0 auto" it will center the block element.
I hope the info above is useful, and if you can provide a link to the page/module in question, I'd be happy to take a look and provide a more difinitive solution.
Rick.