Once you have started your story you will eventually reach a point where you need to add a problem.
Every story must have a charter with a problem. This can be any type but it will decide the resolution of the story. It also should be linked with you charters personality and setting.
People say that you need one big problem to make a story interesting but I believe that you can have a main one and a few small ones that are linked with clues to your resolution.
Clues are more important at this stage but they are important at all stages just they need to be more noticeable.