Scout rank is the first rank on the road to Eagle. To become a scout requires you to be at least 11 years old, or 10 years old with an Arrow of Light (the highest Cub Scout rank) and to have a basic understanding of the Scout Oath and Law.

A full explanation of what is required to achieve this rank...
http://usscouts.org/advance/boyscout/workbooks/Scout.pdf

Tender foot is the second rank on the road to eagle. To attain this rank a scout must:

• Go on a camping trip and help prepare food
• Have a more comprehensive understanding of the Scout Oath and Law
• Prove physical fitness
• Show basic First aid and knot tying skills
• http://usscouts.org/advance/boyscout/workbooks/Tenderfoot.pdf

Second Class is the third rank on the road to eagle. Second Class rank is to point at which some Troops allow a scout to become a Patrol Leader or another leadership position. To Attain this rank a Tenderfoot must:

• Basic orienteering skills
• Cook for the Troop and do all the preparation required
• Participate in a one hour or more service project
• show knowledge of some local plant and animal life
• Have a more in depth knowledge of First aid
• http://usscouts.org/advance/boyscout/workbooks/Second-Class.pdf

First Class is the fourth rank on the road to eagle. First class is obtained by a Second Class Scout when he:

• Show more in depth orienteering skills
• Help plan a trip for the Troop
• Show Lashing skills to make a useful camp gadget
• A detailed knowledge of First aid
• Invite a prospective member to a Troop activity
• http://usscouts.org/advance/boyscout/workbooks/First-Class.pdf

Star Scout is the fifth rank on the road to eagle. A First Class Scout must:

• Earn at least 6 Merit badges (4 must be Eagle required)
• Participate or plan and do your own 6 hour service project (some troops require a scout to do his own)
• Serve in a leadership position in your Troop for at least 4 months
• http://usscouts.org/advance/boyscout/workbooks/Star.pdf

Life Scout is the second to last (sixth) rank on the road to eagle. A Star Scout must:

• Earn 5 or more additional merit badges at least 3 required for Eagle
• Participate in service projects totaling six hours or more (some troops require a scout to do his own)
• Teach lower ranked Scouts skills necessary for their rank
• Serve in a leadership position for six months
• http://usscouts.org/advance/boyscout/workbooks/Life.pdf

Eagle Scout is the highest possible rank attainable in the Boy Scouts of America.The Eagle scout's requirements may be the shortest in length, by they are by far the hardest.

• Earn a total of 21 merit badges, including the 14 specifically required for Eagle
• Serve in a leadership position for six months that is one of the specifically required positions
• Plan, and show leadership in a service project for your community
• http://usscouts.org/advance/boyscout/workbooks/Eagle.pdf