Most probably you are going to be seeing in-country using an air-conditioned bus with a guide or even a tour leader. However, the ideal option is leasing a car. You will find several driving principles you want to follow in Namibia.
Generally, the streets are tarred and well signposted, one can also hire GPS units with your vehicle and the tour operator will supply driving directions to supplement your GPS.
Plan your trip ahead of time in case you're driving; you may require a 4×4 for places where the street progresses toward becoming rock or soil. Car rental is a good option. You can hire 4×4 self drive car rental in Namibia through online resources.
You can also decide on a full holiday package, where you are picked and dropped from the airport terminal, port, and so on in every destination that you visit, and after that just rent a car around the urban areas and make use of daily visits in each area. Car hire is easily accessible within urban communities.
Public transport in Namibia, especially the bus system, isn't perfect nor is the local train unless it is a luxury train. In many areas it is even not recommended to travel by local trains and buses, so make sure you always use your own rented car but rent a car from a reliable company only.
The car rental packages are available from all the major airport car to hire operators at branches across the country.