Spirit Guardians can’t be interacted with, but they are adept at preventing movement through areas they inhabit. Any creature that enters a haunted square must make a DC 10 Wisdom Saving Throw immediately or be frightened-upon a failure these creatures are grappled by the ghosts and cannot leave the haunted squares voluntarily. Creatures in this state can use their action to attempt another saving throw to escape the spirit guardians.
If successful, they may move out of that square on their turn, unless engaged in combat. Spirits then turn it’s attention to any who escaped them last round and continue grappling them until someone else gets grappled by them or enough time has passed for the ghosts essence to fade away. Spirit guardians always appear as shadowy figures of themselves from when they were alive, but seem to fade in and out of view at random.
When ghostly entities take an action to move, they simply stand up or get down from one square to another. Their movement otherwise doesn’t trigger free movement unless somehow an object is dropped or damage is dealt during the actions of the spirits guardians. It’s pretty simple and mostly designed to make it difficult to move things like carts or lowered drawbridge without dealing with the spirits.
Spirit guardians also present a chance for players to interact with their environment in an interesting way: by attempting to speak with them and gain information, knowledge and even treasure from them. This is one of those moments where you as a D&D game master can take advantage of the history that you’ve built into your campaign world and apply it to what’s happening in game. It can be helpful for players but also a chance for them to role-play some more, or even shine as their characters begin to unravel some deep knowledge from these ghostly figures of yesteryear.