What happens there
EA presents The Grounds as a connected social space with a central Terrace and district areas, linking off-pitch gathering to football activities and Clubs. Its launch description names Montclair and Zeiza among the districts. It is a distinct mode, not a label for every stadium match in FC 27.
Sources: EA The Grounds deep dive (opens in a new tab)

Getting started
EA’s introductory guide describes an initial 11v11 warm-up before the Grounds introduction. Follow that in-game introduction to learn where activities and Clubs connections sit, rather than expecting a regular Kick-Off menu to reveal the same space.
Sources: EA: getting started in The Grounds (opens in a new tab)
Check your platform first
The mode and Clubs support PS5, Xbox Series X|S, PC and Switch 2. The full game is also sold for PS4, Xbox One and Switch, but those versions do not include this feature pair.
Sources: EA FC 27 modes (opens in a new tab) · EA editions and release dates (opens in a new tab)
Independent FC 27 guide. Linked official text supports the stated facts; any game imagery is promotional context.