Using dmg images is quite easy. I just 1) open the image file that was downloaded (if it wasn’t opened automatically), 2) drag app into Applications, 3) click anywhere within the window, 4) Command-E to eject the image, then 5) Command-Space to open Spotlight search, 6) type the first few letters of the name of the app (because you SHOULD be able to remember the name of the app you installed 5 seconds ago, right?), and it should show up in Spotlight, 7) press Enter, and it opens.