"Normal phase" and "reversed phase" refer to the relative polarities of the column and the solvent. If the column is polar and the solvent is non-polar, it's "normal-phase" chromatography. If the column is non-polar and the solvent is polar, it's "reversed-phase" chromatography.
An archetypical normal-phase column would be something like "bare" silica gel. An archetypical reversed-phase column would be something like octadecyl (C18) groups bonded to a silica support.
Most "cyano" columns consist of something like cyanopropyl groups bonded to a silica support, That cyano group has intermediate polarity, so if you use it with something like hexane/methylene chloride mobile phase, you will be doing normal-phase chromatography. If you use it with water/methanol mobile phse, you will be doing reversed-phase chromatography. (I would not recommend using the same physical column because of problems changing over between immiscible solvents).
phillipem was referring primarily to the use of cyano columns in reversed-phase, where the selectivity is somewhat different from that of C18 columns due to secondary interactions with pi and non-bonding electrons. The fundamental retention mechanism is hydrophobicity, just as in any other reversed-phase separation; the secondary interactions "tweak" retention a bit to move peaks a little further apart (or closer together!).
The mechanism in normal-phase is somewhat hazier (in my mind, at least); the simplest explanation is dipole-dipole interactions with analyte molecules.
Of course, all of the above explanations are over-simplified
If you can, get a copy of "Practical HPLC Method Development" by Snyder, Glajch, and Kirkland (
http://www.lcresources.com/resources/resbooks.html ). That has much more thorough explanations of what's going on.
The bottom line: you first have to decide what kind of chromatography you want to do (reverse- or normal-phase),
then select the column, not the other way around
