The background of fighting in North Africa begins long before the Second World War with European colonial interests in the region. In the 19th Century, Germany had taken part in a competition of sorts among European nations called the "Scramble for Africa." The Scramble is a short name for the period in which many European powers invaded and colonized nations throughout Africa, acting under the imperial mindset that was a powerful presence in the late 1800s and early 1900s, often called "New Imperialism." Africa was largely untouched by Western markets until the Scrample, and its "untapped" resources proved too valuable for Europe to resist. Rivalry among the powers at the time led to competition among them for territory in North Africa. Germany was one such power, a new player on the imperial stage after its unification in the 1870s. In the 1890s, Germany adopted a policy called "Weltpolitik," under which it aggressively expanded in hopes of becoming a world power. (see Kevin Shillington, "History of Africa," and Thomas Pakenham, "The Scramble for Africa.")

However, following German defeat in the First World War, the allies split up much of Germany's territory among themselves in a series of treaties that proved disastrous for Germany. In North Africa, Britain took much of the territory that Germany had acquired during the Struggle.

When 1940 arrived and war broke out in Europe once again, Britain attacked an Italian military base in North Africa following the Italian declaration of war. Italy responded, but was defeated by the allies, and Britain began to gain control over North Africa. Seeing an opportunity to regain its lost territories, and aware of the need to assist its ally Italy, Germany dispatched the Africa Corps to North Africa under the control of the infamous general Erwin Rommel. Rommel would wage war in North Africa until 1943. (J Butler, "The Mediterranean and Middle East, Volume IV," and the Oxford Companion to World War II.").

In short, the Germans were in North Africa out of a desire to support Italian forces. However, their long-standing colonial interests in the area were a factor as well.

(Thanks to CrossyNZ for posting this question again; to the original poster, I hope this answer helps your out!)