The demo version is fully featured and enough to get you started using the Solved Method. The only restriction is that you can only enter one Solved Plan.
As soon as you are ready for more, you can purchase a license key for the full version to remove all restrictions.
Open the dmg file then move the Solved folder to your applications folder. Open the folder and run the Solved program. If you get a message saying that you cannot open the program then use ctrl and left click to open the file.