This is an idiomatic English expression which is commonly used. It would be very difficult to guess the meaning of this expression without any knowledge of it as it is used in a very metaphorical way.
This expression is used to claim that someone is accusing someone else of doing something which they themselves do. Therefore it is used in an ironic manner to suggest that someone should not judge someone else for something which they too may be guilty of.
The expression is said to derive from the fact that if a pot which is often covered in soot mocks a kettle for having a small dusting of soot this is ironic as they both share this quality.
The earliest recorded usage of this expression can be found in Thomas Shelton’s translation of the Spanish novel by Cervantes, Don Quixote. The translation published in 1620 is titled Cervantes Saavedra’s History of Don Quixote and reads “you are like what is said that the frying-pan said to the kettle, avant, black-browes.”
The first spoken record of this expression dates to the year 1693 by Englishman William Penn who, in his Some Fruits of Solitude, wrote “or a Covetous Man to inveigh against Prodigality… is for the Pot to call the Kettle black.”
An example of the usage of this expression can be found in the title of an article in The Guardian which reads “Pot McEnroe calls kettle black.” The article describes how John McEnroe in his role as commentator stated that the behaviour of Greg Rusedski at Wimbledon was unacceptable despite the fact that in his days as a tennis player McEnroe himself had behaved in a similar way.