(For more screenies, you may want to check out the little tutorials that I've written.)
The first thing you may want to do after installing Recipe Radar is bind a key to toggle its main window. This screenie is taken from the game's Key Bindings interface.
When you bring up the window by hitting your newly bound key, you should see something like the the following pic.
There are two selectable "tabs" near the top of the window. The last screenie shows recipes in the current region (the "radar tab"), while the next one shows all for-sale recipes of a certain profession (in this case, First Aid).
If you shift-click on a vendor, they will show up on the world map. The following pic shows a couple of vendors on the minimap.
Vendors will also show up on the worldmap.
In case you haven't seen a recipe before, it will show up as 'Uncached Recipe'. If your server hasn't seen this recipe, you may be disconnected if you mouseover the question mark icon.