Explained Answer
Some problems that needed to be overcome in order for NASA to be able to land men on the moon and return them safely were, A new, larger rocket had to be developed to get the Apollo Command Module, Lunar Orbiter, and LEM (Lunar Excursion Module) into orbit. Additional engines had to get the whole package on the way to the moon. Eventually, the Saturn V rocket was created to achieve this purpose. Then, there had to be a way to land the LEM safely onto the lunar surface and return it to the Lunar Orbiter.
Short Answer
1. Larger rocket.
2. Additional engines.
3. Way to land safely.