Lion rank is for kindergarten-aged Cub Scouts. To earn Lion, Scouts must complete five required adventures. There are nine elective adventures they may also earn. Adventures and their requirements, along with suggested activities, are in the Lion Handbook. Lions may participate in the Pinewood Derby and go to family camp, but they aren't allowed to go to day camp or use BB guns. Lions don't earn Bobcat (explained below).
All Cub Scouts, from first grade on up, must earn the Bobcat rank before they earn the rank for their grade/age.
To earn Bobcat, the Scout must demonstrate the Cub Scout sign, salute, and handshake, and tell what they mean. Scouts must also recite, with help if needed, the Cub Scout Motto ("Do Your Best"), the Scout Law, and the Scout Oath. Parents or guardians need to go over youth protection materials with their Scout. Also, the Scout must earn the Cyber Chip (for Internet safety).
Tiger rank is for Cub Scouts who are in 1st grade.
To earn Tiger, the Scout must complete six required Tiger adventures and one elective adventure. Adventures and their requirements, along with suggested activities, are in the Tiger Handbook. There are a total of 19 adventures for Tigers.
Wolf rank is for Cub Scouts who are in 2nd Grade.
To earn Wolf, the Scout must complete six required Wolf adventures and one elective adventure. Adventures and their requirements, along with suggested activities, are in the Wolf Handbook. There are 19 Wolf adventures in all.
Bear rank is for Cub Scouts who are in 3rd Grade.
To earn Bear, the Scout must complete six required Bear adventures and one elective adventure. Adventures and their requirements, along with suggested activities, are in the Bear Handbook. Just like Tiger & Wolf, there are 19 Bear adventures that Scouts may earn.
Webelos Rank is for Cub Scouts who are in 4th or 5th grade.
To earn Webelos, the Scout must complete five required Webelos adventures and one elective adventure. Cubs must also be active in their Webelos den for three months. Adventures and their requirements, along with suggested activities, are in the Webelos Handbook. In total, there are 27 Webelos adventures. (P.S. to you: Webelos, a backronym for WE'll BE LOyal Scouts, always ends with an s.)
The Arrow of Light is the highest rank in Cub Scouts. Cubs must be active in their Webelos den for six months since finishing fourth grade or since turning ten years old. To earn the Arrow of Light, Scouts must complete four required adventures and one elective adventure. Adventures and their requirements, along with suggested activities, are in the Webelos Handbook. Completing this rank prepares the Scout for Scouts BSA (i.e., Boy Scouts). This rank is the only Cub Scout achievement that may be worn on the Scouts BSA uniform. Adults who earned Arrow of Light as a youth are entitled to wear a special square knot patch on their uniforms, too.
More specific information on completing ranks can be found in the appropriate rank handbook, or online here (watch the video!).