Print designs are printed using an ink-based color model called CMYK. You won’t be able to print your designs using a light-based color model like RGB because the colors won’t look the same in print as they do on screen.
Some types of design like logos are used in both print and web, so you’ll need to create both CMYK and RGB versions of those designs.
You should always create your print files in CMYK color mode first, not RGB mode.