The screenshots from the video provides a subtle hint to how Free Play in Forza Motorsport 8 will work:
Had to use Google Translate for this one, as German isn't my native tongue, so here:
Freies Spiel -
Free play
Schnelle Veranstaltungskonfiguration - Quick configuration
Erweiterte Veranstaltungskonfiguration -
Advanced event configuration (whether or not this includes custom championships, or if you can hand-pick your opponents' cars remains to be seen.)
Autos kaufen oder mieten -
Buy or rent cars (With the ability to rent cars for Free Play, it's expected that
all the cars in the game are available as rental cars in Free Play. Yes, all 500+ of them - currently at 506, or 520 with the Race Day Car Pack and Forza Editions. Whether or not you can choose from their car-specific colors and do basic setup tuning based on its default specs remains to be seen.)
As always, you can select cars you own in your garage.
Spieltyp -
Game type. So far, it reads
Rundstreckenrennen, literally:
circuit racing. Last I heard, there won't be any drift or drag modes at launch, but there could still be Hot Lap mode.
Strecke -
Route, or in this context,
environment.
Streckenführung -
Route guidance, or specifically,
layouts.
Tageszeit -
Time of day.
Wetter - Weather.
Rundenzahl - Number of laps. One such feature is set to Automatic which gives you a predetermined number of laps, or you could choose how many laps you want the race to last.
Anzahl Drivatare - Number of Drivatars.
On the top right corner of the screen, you can read
Zugelassene Mietwagen which translates to
Approved rental cars, in which, this build features 529 known cars (assuming this does not include the 2018 Porsche 911 GT2 RS Forza Edition), likely also including the Race Day Car Pack (eight cars) and the five Forza editions from the VIP pack.