I also received Azaleas without instructions. I live in a very dry area of Colorado that gets alot of sun. When you say the plant needs to be on a window sill with alot of sun, do you mean south, or east? My north windows rarely have any direct sun, but I fear the south windows might get too hot?
Also what type of fertilizer is best and how often do you recommend using it?
If your Azalea is on a windowsill and the window is completely uncovered, then an east or north windowsill is best. South sun on sunny days is too hot and too intense.
Be sure to keep your Azalea well moistened by watering as soon as the surface of the soil feels almost dry.
Fertilizing it is largely irrelevant. However, it is best to use an acidic fertilizer, such as Mir-acid, at half strength no more than once monthly.
Finally, I will note that it is important to keep your Azalea well pruned to maintain it as a compact, full plant.