When you complete a hidden-object scene you will earn points which will go toward unlocking stars for the scene. You can earn up to five stars on each scene and these stars can then be used to complete tasks later on. In order to maximise the number of points you get and the stars you unlock you will need to replay the same scene over and over again so that you have the item placements fresh in your memory and be able to quickly tap them. You will find this easier to do if work out some kind of order instead of tapping them randomly.