Adobe InDesign offers a lot of features for a desktop publishing program, including those for the professional printer. The program is designed to work with other Adobe products in the Creative Suite series, including Illustrator and Photoshop. If you just plan to print your InDesign document to an inkjet printer, you do not need to change RGB or red-green-blue images to CMYK or cyan-magenta-yellow-black images. The "K" stands for "registration," the professional printer's designation for the black plate. However, if you need to output your document for use on a professional press, you must make this change.
Go to the "File" menu and select "Print." Do this, of course, when you are finished editing your InDesign document and are ready to print or create a PDF of it. On the left side of the "Print" window you will see a list of choices starting with "General" and continuing with "Setup," "Marks and Bleed" and "Output" as well as others. Select "Output." When you do, new options will open to the right. The top option is "Mode," in which you can select "Separations (Host Based)" to allow you to change your document to CMYK output. You can look at how the separations into CMYK will appear by going to the "Window" menu and selecting "Output" and "Separations Preview." You will need to know your professional printing press requirements to set the correct output parameters. These are different from printer to printer. When ready, click the "Print" button.
Select "Adobe PDF Presets" from the "File" menu and choose "[Press Quality]" from the submenu. A dialog box will pop up for you to name the PDF file and place it on your computer where you want it. Click the "Save" button and the next dialog box will appear. When the PDF dialog box appears, select "Output" from the left box and set the "Mode" to "Separations (Host Based)" choice. Insert the correct parameters for the printer and print your document.
Double-click each image in your InDesign document individually. This will give you the option of editing the original in Photoshop, which is the best place to create CMYK separation files for your images. This is because Photoshop is designed to edit and produce the best color for images, whereas InDesign is a desktop publishing program. In Photoshop, go to the "Image" menu and select "Mode." Then select "CMYK Color." Save the image, then update it in InDesign.