is it possible? i bought tis 100 (this is my very first purchase of a game ever) and all I can find are addresses that start with gogdownloader://

Go to your Account screen and hover your mouse over the game, you should see down arrow. Select that and from the drop down menu choose View Downloads. This will let you download the installer, manual and any other goodies that come with the game.

the gog downloader >> https://www.gog.com/downloader however is easier
but its still optional

also keep in mind that the downloader and galaxy are NOT the same

the downloader is just that a downloader
galaxy is a steam like ( wannabe ) client

To download & run the installer without using Galaxy or the old downloader, see the attached images. (I used the Neverwinter Nights installer as the example; ignore the references to Stasis in the descriptive text.)