The first Reichstag, the parliament of the confederation, was elected on February 12th 1867. On April 16th it accepted the constitution, which was essentially written by Otto von Bismarck, the Prussian minister-president and first Bundeskanzler (the sole minister) of the confederation. North German liberals had their influence on it.
According to the constitution, the highest organ of the confederation was the Bundesrat (Federal Council). It represented the governments of the North German states. Prussia had 17 of 43 votes in the council, giving it the right of vetoing. By constitution, the King of Prussia was the President of the council and also the confederation. He installed the Bundeskanzler (Federal Chancellor), the chief of executive.
The Reichstag (sic!, although the confederation was called Bund) was the parliament, elected by all male north Germans above the age of 25. This was quite extraordinary in those times; Bismarck introduced this in the hope that it would create conservative majorities. Reichstag and council together had legislative powers, making the democratically elected Reichstag an important and powerful organ.
After the Franco-Prussian War of 1870/1871, the south German states Baden, Bavaria and Württemberg joined the confederation. It was renamed Deutsches Reich (German Empire), and the constitution of the confederation, with little changes, became the Constitution of the German Empire.