To let people download files, you just need to link to them as you would any other page. For example,
<a href="file.zip">Click here to download!</a>
However, if you want to go more advanced and find out how many people are actually downloading your files (and it is kinda nice to know) you may like to check out DownloadCounter.Com (link below). It even lets you include Top 10 download lists on your site that dynamically update and so on!
Hope this helps - feel free to get back to me with any further questions!