The major differences between sport-pilot and private-pilot certification is that sport pilots can start off with fewer training hours and lower-cost aircraft, then add endorsements as their interest and training expand. The sport-pilot certificate gets you flying faster! Let's take a look at how sport pilots can spread their wings with endorsements.
An earlier Flight Guide covered controlled and uncontrolled airspace. Specifically, it outlined the requirements for flying in Classes A, B, C, D, E, and G airspace. You learned that sport pilots cannot fly in Class A airspace (above 18,000 ft. mean sea level (MSL) and that they can't fly in Class B, C, or D (tower-controlled) airspace without an official endorsement in their logbook that says they can.
Why is this so? It's because flying in these controlled airspaces is more complex, requiring an understanding of air traffic control (ATC), radio communications, and other more advanced topics than pilots in Class E controlled or Class G uncontrolled airspace need. As a sport pilot you can legally fly in Classes E and G all day long (no night flying, remember) and that might be enough for you. If it isn't, it's time to get some more training.
If you want to add a tower-controlled airspace endorsement, all you need to do is prove to a flight instructor that you can do it. That means reviewing the requirements and limitations of these tower-controlled airspaces, learning more about communicating with ATC, making sure your aircraft is equipped to enter controlled airspace, and showing your instructor that you know this stuff. You already had to know the basics of controlled airspace for your knowledge test so you might need just a refresher course. Your instructor will go with you as you fly into, land, and take off at airports in Class B, C, or D airspace.
Frankly, some sport pilots decide to get this endorsement out of the way quickly. If you'll be flying in, near, or through tower-controlled airspace as a student, consider opting to get the endorsement as soon as you get your solo permit. It should take you only a couple of extra hours of training, so you might as well do it while you're focused on being a student pilot.