Just read any SPAB damp related pamphlets for basic info. If you want it explained more, check out the periodpropertyuk forum. Its not a trivial subject though.
There are plenty of people making common wrong assumptions, a classic one being that damp moves from the outside of a house inward, and thus coating the outside helps. In fact overall vapour movement is from inside to out, and coating the outside increases water content in walls by blocking evaporation. There are several common misperceptions on this topic.
NT