[1] Germany gained the islands of Heligoland (German: Helgoland) in the North Sea, originally possession of the dukes of Holstein-Gottorp but since 1814 a British possession, the so-called Caprivi Strip in what is now Namibia, and a free hand to control and acquire the coast of Dar es Salaam that would form the core of German East Africa (later Tanganyika, now the mainland component of Tanzania).
[2] In exchange, Germany handed over to Britain the protectorate over the small sultanate of Wituland (Deutsch-Witu, on the Kenyan coast) and parts of East Africa vital for the British to build a railway to Lake Victoria, and pledged not to interfere with British actions vis-à-vis the independent Sultanate of Zanzibar (i.e. the islands of Unguja and Pemba).
The German East Africa Company under Carl Peters had acquired a strip of land on the Tanganyikan coast (leading to the 1888 Abushiri Revolt), but had never had any control over the islands of the Zanzibar sultanate.
With the construction of the Kiel Canal from 1887 onward, control of the German Bight had become essential to Emperor Wilhelm's II plans for expansion of the Imperial Navy.
Wilhelm's naval policies aborted an accommodation with the British and ultimately led to a rapprochement between Britain and France, sealed with the Entente cordiale in 1904.