Get the latest installer from the product page.
Like most macOS applications DropPy is distributed as a dmg image.
Mount the downloaded
DropPy.dmg file by double clicking it in Finder. In the appearing window drag the DropPy icon to the Applications folder.
DropPy is now installed and can be started from Launchpad or from your Applications folder.
You can now unmount and delete the dmg file.
When starting DropPy for the first time macOS will ask you if you are sure you want to open it. Select Open.
Then the First Run Assistant will appear. In four steps you will select a Workspace folder and learn about what you can do if problems occur.
The First Run Assistant will then close and DropPy will be shown, ready to receive your first item.
If you want to revisit the First Run Assistant after initial setup has been completed you can start it again in the Help menu.
The step where you selected a Workspace folder will however not be editable any more. Use the Workspace section in Preferences to manage your Workspace afterwards (more info).