See: Reykjavik#Get in
Keflavík International Airport is the main international airport in Iceland, and the point of entry for most people arriving in Iceland. It has direct flights to various destinations in both Europe and North America. Reykjavík also has an airport with flights to locations in all parts of the country, as well as to Greenland and the Faroe Islands. Note that Keflavík and Reykjavík airports are separated by about 50km, and although the international airport is often referred to as Reykjavík Airport in international flights, in Iceland Reykjavík Airport will be understood to be the domestic airport.
If you arrive in Iceland on the ferry from Denmark or the Faroe Islands, you will find yourself in Seyðisfjörður, East Iceland. From there, it's a 700km drive to the Southwest. It can be very complicated to get from East Iceland to Southwest Iceland via bus, and you will likely need to stay a night in Höfn, but if you're arriving with the ferry you can bring along a car.
There are busses from most of the main towns in West Iceland, South Iceland and North Iceland to the Southwest.