How does scoring work?
Basically, you earn points by making moves. Make moves in quick succession and you will build up a combo bonus. The combo bonus can significantly increase your score.
You decrease your score when using help. Each button under help (to the left of the board) provides a different kind of help all costing a different amount of your score. They are arranged in order, the cheapest help being on top.
The difficulty of a puzzle relies heavily on the amount of white space logically connected to an available move. Some moves are found with different logic than others and some of these lines of logic are considered more difficult and scored up.
Thousands of puzzles are produced in the lab and their scores are analysed so that the difficulty bar you see below the board reflects an accurate and studied difficulty result.