When you say you "ordered Garmin Topo 24k", do you mean you just purchased one region? There are a bunch of separate disks, each of which only contain a few states. They do not yet have coverage for the full US. In fact, they just got around to releasing the NE 24k topo about a month ago. I think it would cost around $1,000 to buy all of the 24k topo maps!
Many of the maps here will have Mac installers. You will have to decide what is best for you. The Garmin 24k topo's have fully routable roads and most (maybe all?) of the maps here do not contain routing information and can't be used to give directions. The Garmin maps should also have extensive POI's included (like stores, gas stations, etc) which you are not likely to find on the maps here.
I don't think there's much involved with "getting started" here - just browse through the maps and download any that you like. Welcome to the site and enjoy the new GPS!