Original: In 1956, upon formal establishment, East Germany's armed forces were named the Nationale Volksarmee (National People's Army), most of whom, with materiel, were incorporated to the present-day Bundeswehr when the German Democratic Republic was incorporated to the Federal Republic of Germany in the German reunification of 1990.
Simplified: When East Germany (the German Democratic Republic) was incorporated into "West Germany" (the Federal Republic of Germany) in 1990, much of the Volksarmee  property and some of the staff were also incorporated into the Bundeswehr.