Concerning the origins of the name. Of course, the family name’s purpose was originally (before it became necessary for administrative/registration purposes) to identify precisely an individual in a community where the number of christian names was rather limited. You needed to specify which “John” you were talking about, since there could be several of them. Out of my head, some of the ways a name could be adopted (there are certainly many more) :
-The guy’s job, if, it allowed to identify him precisely. That’s the reason why there’s so much “Smith” in the UK, or “Lefebvre/Lefebure/Lefebre” (meaning “smith” in old french, though not in modern french) in France. Firstly, there was a smith in essentially every village. Secondly, there was generally only one. So, you could pinpoint precisely the individual and this job’s name has often be used as an “individualizing” name, later becoming a family name. And the fact that generally, at these times, a job was passed from father to son made even more likely that it would stuck as a family name. On the other hand, you won’t find many “Mr Glassmaker”, because such a job would have been very rare at the first place, nor many “Mr Farmer”, because since the wide majority of the population was farming, it wouldn’t have helped identifying a given person.
-The guy’s noticeable physical feature (Black, Short,…)
-The guy’s noticeable personnality trait (I’ve no such example in english out of my mind, but surely you could find many).
-Sometimes a derogatory nickname, as noted above. The french equivalent of “Bishop” is apparently generally considered as being originally a reference to a haughty attitude (rather than someone being the son of a bishop, of course). It could be true also in english.
-The guy’s location (Wood, or the extremely common french “Dupond”, “Dubois” meaning “from the bridge”," from the wood").
-The guy’s place of origin : either a nearby hamlet or a longaway town, county, or province. If you’re called after the name of an existing place, it’s likely that at the time names became fixed, one of your ancestor moved to this place (the location’s name had to be long away enough, or else, there would be too many people coming from there to identify the person, but close enough for the place’s name to be known : the guy could get the name of a province if he moved hundred of miles away, or of a hamlet if he moved only a mile away)
-A particular event or feat in the guy’s life (like the “King” mentionned above).
-A plain christian name, in particular for abandonned children whose parents were unknown : the day’s saint name was often given to the child.
-Simply the father’s name : Johnson
Actually, anything would do, as long as it allowed to know precisely to whom you were refering. And once again, before the custom and/or the law made family names widespread, this “second name” could change from one generation to another, or even during one’s lifetime.
Finally, note that name can have changed over time, the speling in particular, but also possibly the pronounciation. And also that the original meaning could make sense only in an old version of a particular dialect.