This will set the block that the player using the flint and steel is in to cyan wool. To detect what direction the player is facing and place a block in that direction, you will need to use 4 different command blocks each testing for different ry and rym parameters in the target selector in the execute command.
"score_OBJECTIVE=1" looks for maximum, so a score of 1 and lower. "score_OBJECTIVE_min=1" is minimum, meaning a score of 1 and higher. You can add both of them them to look for a range or an exact score.