Prates is downloading.
Open the Prates disk image in your Downloads folder. Its name starts with Prates and ends in .dmg.
Drag Prates to Applications. If the Mac does not let you, for example on a work Mac without administrator rights, drag it to the Applications folder in your home folder instead.
Open Prates from Applications and sign in with your email address. The seven-day trial starts then, with no card needed.
If the download did not start, download it again.