Imagine a bigger-than-normal bathtub, so you can sprawl-out ( arms & lega akimbo ) without hitting the sides..
the water-density is upped with brine, instead of plain water ( the float-tanks place I used to go to used sacks of "bitter salts" & the texture of the brine was damn-near oily, and DO NOT EVER shave shortly before going into a brine-soak, or you're going to discover what stinging really means )
also it is brought up to a person's body-temperature, or close to it.
When there's no temperature-difference, & you're floating sooo high that drowning is much less likely ( the Dead Sea is probably the prototype for all float-tanks, btw ), & you aren't bumping into the walls, then you're in blissful sensory-deprivation ( total dark, too, obviously, probably use a timer, limit it to 2h max ), & meditation can be awesome in these conditions.