The goal of the game is to connect numbers in the grid with the operators provided. The arithmetic expression must evaluate to the target sum.
Tap an operator to select it, then tap the available spots in the grid to place it.
A green grid cell means that expression must contain the number. Usually at the head of it (but not necessarily).
In some levels, there will be no such green nodes, so it's up to you to figure out where to start the expression.
Both touch screen, mouse controls or track pad can operate this game in the same way.