A: The way in which a character prefers to solve problems effects how the character will go about solving problems in the story, as well as influence how "comfortable" or "uncomfortable" he is as a player in the Overall Story. It also helps "place" him in the appropriate domain on the structural chart so that what he is dealing with personally is consistent with the perspective he has. If he is a Do-er, then he's likely to see (or be seen with) problems in situations or activities. If he is a Be-er, he's likely to see (or be seen with) problems in fixed attitudes or psychological manipulations.
While storyforming in the software, you can easily skip this question if neither choice jumps out at you as being the right one. It's most likely that some other choices you make later on will infer the choice for this one down the line.
Keep in mind that when making this choice, it has a specific context which is this:
When approaching solving personal problems (conflicts) in THIS story, which method best describes your Main Character's preference? In other stories or in other contexts, the character might behave differently, but in THIS story how does he/she behave?