Units, also known as credits, are the main form of intergalactic currency used across many planets.
The crime-lord named Zade Scraggot hired Rocket Raccoon and Groot to retrieve a package with a family of Scalluscs being held in the highly secure "Uptown" section of the Hub for a thousand credits. But upon learning that the Scalluscs had money and could double Scraggot's pay, Rocket and Groot rescued the Scalluscs from their cruel fate after a brief scuffle with Scraggot and his men.
When Rocket told Peter Quill that he would need the prosthetic leg of an inmate in order for them to escape the Kyln, Quill paid the inmate 30,000 units for it. Rocket later revealed that he was joking and did not need it.
The Collector offered four billion units to Gamora for retrieval of the Orb. However, she offered to split this payment with Rocket Raccoon, Groot, and Star-Lord before their escape attempt from the Kyln.