CMYK is a color profile for design files. The letters stand for Cyan, Magenta, Yellow, Black. These are the four colored inks that are used in our printing process, so we need your artwork files set up with the CMYK color profiles. RGB is another common color profile, but is meant for screen presentation (e.g. websites), not printing on physical material.
Go to File > Document Color Mode and select CMYK Color.
Go to Image > Mode and select CMYK Color.
All Spot colors need to be converted to Process before submitting any artwork files. From InDesign, Illustrator, and Photoshop, you can convert a Spot color to Process by selecting Process in the Color Type dropdown.