Both are animated shows, Clone Wars is 7 seasons long and a movie, Rebels is 4 seasons long and is a semi-sequel but not really. Both shows start off aimed at young teens but both become much more mature and honestly both are highlights of Disney Star wars. If people are interested in Disney EU it's definitely worth checking out both
There are lists you can follow online for the relevant plot lines connected to The Mandalorian and Ahsoka. You don’t have to watch all of clone wars. You could potentially get away with not watching all of Rebels but that is a different type of show.