Importing goods can be done at any of the Port icons on the map (There are 2 in Everon).
When driving any vehicle in the vicinity of the port location (marked exactly by the map if you zoom in), you can use the "Vehicle Menu" (Shift+U on PC, left trigger plus D-pad up on a controller) which will give an option to Import.
The port lists goods rather than vehicles. By default it offers everything sold at any non-vehicle shop in the world, and nothing belonging to the occupying faction.
At the top level of the Trade skill you also gain Illegal Imports, which widens the list to every non-occupying-faction item in the game rather than only the ones shops carry.
The port screen shows your money and an alphabetical list of importable goods with their prices. Items are bought in bulk, ten or a hundred at a time, and they are delivered straight into the vehicle you arrived in, so the practical limit on one run is how much that vehicle can carry. Anything that does not fit is not charged for.
Port prices are the item's flat catalogue price. Unlike a shop, the port does not move prices with a town's stock or stability, and the Trade skill's discount does not apply here, so a port is neither a bargain nor a markup: it is the plain price, in quantity, wherever you happen to want the goods delivered.