Rough simplification: Everything that emits light is propably RGB and printed media is CMYK.
Big exception: Home printers use subtractive RGB instead of CMYK because it's cheaper.
Anyway, RGB is based on emitting light, it's a additive (light emitting) color system. The more photons you mix the brighter it gets.
CMYK is a subtractive (light-eating) color system. The more color you use the darker it gets.
Cyan, Magenta and Yellow aren't enough to produce dark colors.
That's why Key (black) is added. However this can result in high ink usage.
Usually the total ink coverage (TIC) is mangaged by ICC color profiles.
Other synonyms: TIL - Total Ink Limit, TAC - Total Area Coverage
For documents you want to keep it between 260% and 330%.
Each print cartridge can print up to 100%. So with CMYK the theoretical maximum of TAC is 400%.
Ask your printery what profile and TAC they expect you to deliver if they don't handle the conversion themselves.
Read more about ink reduction in the PDF export section.
The maximum of available cartridges is often shorten by saying [number]c like e.g. 4c.
Since a piece of paper has two sides the first mode refers to the front side and the second mode the backside.
So, 4c/4c is four-color mode for both sides, while a 1c/0c is a frontside in black (or any other, single color) and an empty backside.
You can use special colors (spot colors) such as metallic inks (e.g. gold as Pantone 871 or silver as Pantone 877) in addition to CMYK however this is going to be very costful.
Open your color switch and unfold the options to create a new color field. You probably want exchange CMYK library for an Pantone or HKS library.
In doubt ask your printery first if they can provide such color and if it can be used on your product.
Coated paper allows more ink usage and prints finer lines.
Uncoated paper is either used for low-quality products or paradoxically for products that are meant to look more prestigious or elegant.
The term coated and uncoted is also often used in pantone library names and file names of ICC color profiles which makes it easier to pick the right one.
Your data is printed on a defined area and then cut out.
The knife can accidently cut into white paper due to little intolerances.
So your print area has to be a little bit bigger than the area of the final product.
This safe area is typically 3 or 4 millimeters wide at each side.
This is the "bleed".
You can't save images in DPI. But you can save in PPI (pixel per inch).
Your pixels will be converted to dots during print production (imagine them as sub-pixels).
As a non-printer you have nothing to do with DPI. Just remember PPI. And 300 PPI for documents still makes a good rule of thumb.
For common document formats you need 300 PPI because your eyes are only an arm's length away.
As bigger the distance the less PPI you need. For posters its about 150 PPI.
When you work with InDesign you can completely ignore the PPI value of your source images.
Because the final PPI value depends on how small or big you scale the image.
InDesign calls this the "effective PPI".
The effective (final) PPI depends on image's pixel count and its scaling on the doument.
You can preview the effective PPI by enabling the option in the links tab.
You can sort by PPI. That way you know what images should be replaced by a higher quality variant that has more pixel.
Don't be afraid of too large source images. InDesign will downsample them if necessary. Default maximum output for colored images is 300 PPI.
If you need PDFs with more PPI, open the compression section in the PDF export mask.
You can do a "soft proof" with them. The profile simulates paper color and ink on your monitor.
They handle the conversion from one color system to another, e.g. from RGB to CMYK.
The profile can also cap the ink limit to let's say 300%. Each profile has its own TAC. Look it up if you need.
Be careful with the export settings. Also, you probably want to double check the total ink after PDF export.
For professional printing you need a PDF/X.
For a dinasour printery you will still need the oldest standard PDF/X-1a:2001. Ask what standard they can process.
With InDesign an RGB workflow is okay as you can do the CMYK conversion on export.
Or would you really want to convert all your hundreds of photos in Photoshop by hand?
If TAC reduction fails occasionally, you can still do the CMYK conversion by hand and export the PDF again. This is often the case with InDesign CMYK vector objects and shadow effects.
While batch conversion is nice for photos, you should create logos in CMYK. It's better to avoid color drifts when it comes to stuff like Coporate Design.
Profile-based ink-reduction is only carried out when a conversion happens.
To be clear: the destination profile (chosen in PDF export) must be different than the profile of the individual image.
So if an image is already using the correct profile but has too high TAC, its profile needs to be changed (if you don't want to change the TAC by hand in Photoshop).
Right-click image object, click Images, then Color Setting of Image and assign a new profile.
Note to self: Need to look up the English names of menu entries.
Acrobat Pro: This doesn't work with the "reader", you need really need a non-reader version.
With Pro version you can do a checkup for PPI, TAC and many more things.