The medium set is a pack of 3 needles, in 3 different sizes.  They are appropriate for sport to worsted weight projects.

The fine set is a pack of 6 needles, in 6 different sizes and lengths.  It would be appropriate for fingering and lace weight projects.

The thick pack is a set of 3 heavier gauge needles, in 3 different sizes.  This set is best suited to worsted to chunky weight projects.