While that's fine if you do it manually (and have the patience of Job) most folks use software -- but I'm getting ahead of myself
This article from our wiki (links are always blue) has links to just about everything you need to know to get started - trunking concepts (always a sticking point for newcomers), USB cables, our DMA FAQ (which covers several topics the Easier to Read manuals don't) and more...
Program your DMA Scanner - The RadioReference Wiki
You might profit in going to the
NY forum once you get the cable and software installed and ask for a file for your application (FreeScan is the way most folks start off). Be very specific about what you are trying to hear - keep in mind the 15X cannot decode anything that's digital in nature
HTH....Mike