Hey! There are several types of icons, I will outline the common ones below:
is a regular airport (there's a similar version with a H for heliports).
The yellow equivalent of that icon that you see whilst in flight is a product recommendation from OrbxDirect (you may need to enable recommendations in the map settings panel on the right):
These are products that are not in your library but are nearby as you are flying around, and available for your current simulator. We also take into account any discounts your account might be eligible for. We also, from time to time, run special discounts for Premium members, and these are indicated with a special badge on the product.
Clicking the icon will open the airport card, and then at the top you can browse the products available there and click any of them to navigate to OrbxDirect.
Does this answer your question? I'm glad you are enjoying Volanta!