Professions, careers and trade level (confused)

[TheSexyYeti]

Can you explain the profession, career and trading level in the config?. I'm trying to change the villagers trades to only accept the coins from the ordinary coins mod instead of emeralds. In the example the profession says 5 and the career says 1. Are all the games profession and careers signified by a number?. Is the level like a weighted chance?. And finally do you have to remove the quotation marks for the game to recognize the changes?.