West Point exists to educate and train Cadets who are commissioned as Officers in the US Army upon Graduation. The commitment is for a total of 8 years, 5 of which are on active duty and 3 in the Reserves if you choose not to continue on active duty. A very few graduates may select commissioning in other services, primarily where one of their parents has served a career in another service.
The primary options for Army service are the choice of branch of service. You choose that at the beginning of your senior year. What are your army career options? After graduating from West Point, you will be commissioned in one of several Army branches. You may want a combat arms branch such as Infantry, Field Artillery, Armor, Air Defense Artillery, Aviation or Combat Engineers. You also may choose a combat support branch such as Signal, Military Police, Chemical or Military Intelligence.
You may also want to choose one of the combat service support branches such as Ordnance, Quartermaster, Transportation, Adjutant General or Finance. Opportunities are also available for the Medical Service Corps or the Judge Advocate General Corps later in your service career. You will advance to positions of greater responsibility in each branch based on your abilities.
West Point is looking for well rounded young men and women who want to serve as commissioned officers in the US Army. By well rounded I mean good students, good athletes, and good leaders. The focus is on service in the Army rather than on the college education part.
Now to answer your specific questions. Commissioned officers serve as leaders of the wonderful young men and women in our Army today. The military is organized into branches of service that are either directly involved on the front lines (infantry, armor, field artillery, etc) or operate in support roles (signal, ordnance, intelligence, aviation, etc.) I would go to the Army's web site and check it out thoroughly.
As for percentage rates for West Point, there are two interesting numbers. The first is the percentage rate of acceptance of offers of admission. In recent years (since 9/11) the percentage rate has been steady at about 85%. That is the highest acceptance rate of any college or university in the nation, topping Harvard, Princeton and all the rest. This says that those who apply to West Point know what they are doing and are very serious about it.
The second percentage rate of interest is the graduation rate. In recent years the graduation rate has held steady between 75% and 80% of those who enter graduate, in four years. The national average is 50% in SIX years.
If you chose not to stay beyond your five year active duty commitment the world is open to you. Experienced young Army officers are in great demand everywhere in our business world and they have no problems supporting themselves or their families.
Finally, to answer your question about the potential for playing a professional sport following graduation. The Department of Defense has recently adopted a policy where a small number of Service Academy Graduates (not just West Point) to be released early from their active duty obligation to play professional sports. They do have to pay back the cost of their education (several hundred thousand $$) and serve in the Army Reserves in a recruiting role, but today there is a viable option for elite level athletes.
If you work for what you want then some day you will get it and when you do you will look back on your days at West Point and thank them for giving you the change to become something better to do something better with you life.