This is a very large question to answer; precisely WHAT do you want to hear? Be more specific!
You will need a few things first - I would highly recommend starting with the Easier to Read manual for the 396. You can either download it, or order it from Scanner Master. Both are linked in the Uniden DMA FAQ which is in our wiki here (anything in blue is a link)
Uniden DMA FAQ - The RadioReference Wiki
Next, unless you are using an older PC, you will need a USB/Serial converter if you wish to use software to program it (it is possible to do manually, but you're going to find that it's a real bear to do - and we'll get to the freeware in a minute). While Uniden sells their USB-1, there are several off the shelf units that are also known to work. They are listed, along with hints using Device Manager, here...
Connecting scanners via USB - The RadioReference Wiki
There is freeware called
FreeScan that will allow you to program the scanner, and pull data from our database (more on that in a moment). The user guide is also hosted in our wiki below...
FreeScan User Guide - The RadioReference Wiki
Finally there are a couple of ways to get data for FreeScan to use. Go to the WV forum and ask - be specific that you are using a 396 and FreeScan. This software can import files from the Uniden Advanced System Director (UASD) or ARC (BuTel) files. You can also use EZ Grab to copy data from our database directly into the scanner editor. The other way is to import data using the web service, which requires a subscription as detailed here...
Premium Subscription Information Page
I would suggest starting with the Easier to Read manual (don't use the Uniden one) - learn about DMA and the basic operations you will need. No matter what software you choose (FreeScan is not the only one...), you need to understand about DMA before you go forward
best regards..Mike