If the solver is opened a new solver GUI is shown under the main game view. The solver GUI looks like this:
You can select the solving method the solver is to be using for solving a level:
Note: The difficulty to find a solution increases from top to bottom of the offered methods. This means selecting "Any solution" results in the best chances the solver to find a solution and "Move optimal with best pushes" results in the worst chances to find a solution.
You can specify which levels the solver should try to solve:
If more than one level is to be solved the solver opens a new window while solving showing the current status of the solving process.
At the bottom of the solver GUI you see a status bar showing the solving process and the time already used for solving a level.
You can close the solver by clicking the close button at the top right of the solver GUI.
Note: the found solutions are stored in the levels they have been found for. After a solution has been found you can close the solver and then select the solution in the solutions sidebar for taking it as new history.