John is a syndicated columnist.
what does that mean when combined? Does it mean that John works in different news channels. I know the dictionary meaning of syndicated but ....
Please approach easy-to-read method
It means that John's column is reproduced in multiple newspapers - typically in geographically separated markets. The implication of the word syndicated is that a group of newspapers that publish his content function as a 'syndicate' - at the very least they make at least some of their content-purchasing/sharing decisions at a group level.
John may work directly for one of the newspapers that is a member of the syndicate, however given the subtle nuance of the term, it is perhaps more likely that he is a 'free-lancer' (ie. he is self-employed). 'News channels' idiomatically refers to television news - not a particularly good fit with the term 'column'.
John's columns are "picked up" by a "syndicate" (such as "United Features Syndicate") and distributed to a large number of newspapers. Instead of being read by just (some of) the 50,000 to 300,000 people that subscribe to John's newspaper, John is read by millions of subscribers to dozens of newspapers.
This makes John famous -- and might make John rich. Thus, there are lots of columnists who would like to be "syndicated columnists". Thus, John is somewhat proud of being a "syndicated columnist", instead of just an ordinary newspaper columnist.