To become a legend of Night City you need reputation, and to build reputation, you need work hard for it. Fixers, solos, netrunners, all want the same. The more gigs you do, the more people hear about you, that's when your street cred will rise. NC is a city of opportunities, you just need to get out there and seize them.
Gained by completing missions and other activities, the amount you obtain can also vary depending on how you complete a quest. Some items, such as the Samurai Jacket, passively increase the amount of cred players can accumulate.