Challenges are similar to other problems - you submit solution which is either accepted or not.
However, such problems could be solved with various degree of success - i.e. checking system calculates some "score" for your solution. These scores are shown in dedicated tables for every challenge problem.
In the past such score points added some bonus to user's overall "enlightenment" but I believe this feature was turned off because "weights" of such bonuses were purely artificial and this was feeling unjust.
So nowadays we simply enjoy such "challenges" in friendly manner, they do not affect overall score (it only matters that solution satisfies some minimal criteria).
Here are two examples of these: Color Cubes Advanced is about playing a well known game and Brain Fibo asks you to optimize Brainfuck code.