An German blue card is a residence permit issued in the EU uniform format. It looks like other German residence permits (that is, it's not physically very blue, though some of the background pattern is blue) except for the annotation
BLAUE KARTE EU.
As a uniform-format residence card from a Schengen country, the card allows you to enter the Schengen area when you present it at the border, together with your valid passport or other travel document.
There shouldn't be a need for other documents. If you transit another Schengen country on your way to Germany, you may be asked to explain what you're doing there, but "I'm in transit towards Germany where I live" would be a fully sufficient answer to that.