Hi Fantalove,
I am assuming you are asking how your friend can get tax exemption status for the items he wants to ship to Ethiopia, correct? If so, basically he will have to contact the Ethiopian embassy in the US and provide them with itemized list of goods he wants to take to Ethiopia. They will then write a letter of support for tax exemption for him. This applies only to Ethiopians and those who hold Ethiopian origin id cards, and it is done as an added incentive to encourage them in returning to their home of origin.
However, as far as i know personal vehicles are no longer allowed tax exemption status, unless it has something to do with his field of work - which might get tax exemption. In any case advise your friend to contact the Ethiopian embassy and they will walk him through the process.