Welcome aboard CompD
PM = Private Message, sent to someone specifically for them to see.
Bump = is forum speak for moving a thread to the top of a give forum (and hence being more likely to be noticed by other users). For the most part a bump after a day or two of not getting much of a response is ok, but continual bumping is silly. Also we generally prefer users to try and post a more constructive reply than bump when bumping a thread such as new things they may have tried or thoughts they had on an issue etc.