Mine came with a manual in German and some hardly readable photocopy of a translation written on a typewriter. That was a steep learning curve for a kid. Fortunately there were a lot of young and older folks who shared knowledge, engaged into demo scene or just played games. Later on I got a couple books and subscribed to the C&A magazine which helped me a lot with diving into graphics programming, extension ports, SID, etc.

The best part about C64 was it immediately booted into a Basic prompt that invited you to experiment with the hardware, like typing these magic POKE commands to set screen and text colors.