There are four different jerseys in the tour. as the other person said there are Yellow, Green, Polka dot and white. After each stage they award these jeresys, as they might change from day to day.
Yellow is most famous and is for the person with the fastest time over the duration of the race.
Green is the points leader. there are sprint points all along the flat stages. the people who cross those lines first get points. and also at the end of the stage whoever gets first gets alot of points too.
The polka dot is the same as the green except flat sprint points the points are at the top of climbs. the first over the climb gets the most points.
the white jersey is the yellow jersey but it is for the fastest rider who is under 25 years old. it is the best young riders jersey.