On August 11, 1919, the Weimar Constitution was signed, signalling the birth of a new German republic.  

The German people, united in all their racial elements, and inspired by the will to renew and
strengthen their Reich in liberty and justice, to preserve peace at home and abroad and to foster
social progress, have established the following constitution:

Das Deutsche Volk, einig in seinen Stämmen und von dem Willen beseelt, sein Reich in Freiheit und
Gerechtigkeit zu erneuen und zu festigen, dem inneren und dem äußeren Frieden zu dienen
und den gesellschaftlichen Fortschritt zu fördern, hat sich diese Verfassung gegeben.
Opening statement,  The Constitution of the German Empire. dated August 11, 1919.

Centenary of the Weimar Constitution
Issued by German post office in 2019
Designer: Jens Müller

The Kaiser fled Germany in November 1919, leaving behind a country in chaos. Wilhelm abdicated when faced with mutinies, the German Revolution, hyper inflation, food shortages, and people uprooted from their lives agitating for significant changes in how the government was run. A provisional government was formed to halt  to fill the power vacuum. 

The new government, charged with of hammering out a new constitution for the war racked people, was extraordinary in its inclusiveness:

On 19 January 1919, the Constituent National Assembly was elected. For the first time, all Germans from the age of 20 were able to participate in this election. It was a general, equal, direct and secret election. Now the majority but proportional representation no longer applied. The SPD had been calling for this since 1891 because it had always been disadvantaged by the majority voting system and the run-off system. The proportional representation system, which is still in force today, was even given constitutional status. 

In addition, the German Reich was one of the first countries to introduce the right to vote and stand for election for women. In addition to 386 men, 37 women belonged to the National Assembly. The voting age was lowered from 25 to 20 years, so that 36.3 million people were eligible to vote, 83 percent of whom also went to the polls. An important difference to the current system was that there was no barrier clause. In addition to the six larger parties, three splinter groups were also represented in the National Assembly, which received a total of only 1.6 percent of the votes and sent a total of seven deputies. This fragmentation increased continuously, so that in 1930 15 different parties and groups were finally represented in the Reichstag. Constitution of Democracy 1918/1919 | Weimar Republic | bpb.de

The provisional government moved out of Berlin, the site of running gun battles as rival factions fought in the streets. The city of Weimar was selected for its relative safety for all the government participants. The government quickly set about creating a working constitution. 

The Weimar Constitution (WRV)13 was born in opposition to two models: The German Empire’s constitutional monarchy and post-revolutionary Russia’s concept of a soviet republic.14 Although there
was strong political support for each of the two concepts, with national-conservatives (e.g., DNVP) on the one and socialists (e.g., USPD) on the other side, a large centrist majority (e.g., SPD, CVP, DDP) chose to abolish the monarchy and incorporate some of its key features at the same time.

The Weimar Constitution Germany’s first Democratic Constitution, its Collapse, and the Lessons for Today Robert Poll
This is an exceptionally clear accounting of the creation and collapse of the Weimar Republic. An excellent starting point if you are unfamiliar with the era.

The new constitution was formally adopted by the government in a vote of 262 votes to 75. In late summer, the Weimar Constitution was signed into law, changing the government from a monarchy to democratic parliamentary republic, retaining the original spirit of the provisional government.

Article 1 of the Weimar Constitution laid out where the government derived its power: 

The German Reich is a Republic.
Political authority emanates from the people..
Das Deutsche Reich ist eine Republik.
Die Staatsgewalt geht vom Volke aus.
ghi_wr_weimarconstitution_Eng.pdf (ghi-dc.org)

The constitution went further and ensured women had equal rights under the law.  

Article 109 paragraph 1 stipulated: “All Germans are equal before the law. Men and women basically have the same civil rights and obligations.”
Constitution of Democracy 1918/1919 | Weimar Republic | bpb.de

It was a short-lived experiment in democracy. The country remained fractured by competing political interests both on the streets and in the government. Coup attempts, assassinations and extremist street warfare continued.

From the very beginning, the newly founded republic must assert itself against enemies from the right and left who reject its basic democratic principles. While the Communists want to establish a Soviet rule based on the Soviet model, the right-wing camp includes völkisch and nationalist actors such as the newly founded NSDAP in addition to the old monarchist-minded elites. In some cases, civil war-like conditions prevailed, which reached their climax in the crisis year of 1923.
Ernst Piper, Embattled Republic 1919-1923

The Republic struggled along, increasingly weakened by the left and right, until the slow steady rise of fascism brought the Weimar experiment to an end in 1933 with the election of Hitler. If you’d like to read more, I recommend Piper’s lengthy dive into the Weimar years. Its in German, but translates very well. Detailed and approachable in its delivery. The BPD also offers it free, in a pdf format.  Start here: Weimarer Republik | bpb.de Don’t forget to check out the AWESOME source texts he includes.