There are three types of Summon Scrolls that you can use at the Summon Gate.
Basic Summon Scrolls are used to summon Heroes of 1-5 stars.
Royal Summon Scrolls are used to summon Heroes of 3-5 stars.
You get one of these over a certain period of time, as a reward for completing various quests, or by purchasing one with Gems.
NOTE: The rolling pictures of Heroes are just examples of possible summons you may get. The hero you get does not depend on the specific timing of your summon tap.