It's very unlikely you'll be able to print white.
White ink is a very specialised thing - most professional printers won't have it. It's only really ever used for printing to acrylics, and even then sometimes it's just a white coating that the other colours are printed onto.
You cannot make white from other inks.
CMYK inksets use subtractive colour to mix other colours from the spectrum (essentially C+M = Blue, M+Y = Red, C+Y = Green, C+M+Y = Black, but Black is used to reduce ink usuage and white is the absence of colour)
RGB light uses additive colour to mix other colours (You don't get such a simple transition from RGB->CMYK primaries, but white is R+G+B and black is the absence of colour)