Depends on the school and what is going on during the visit, but it’s a way for the school to roll out the red carpet and put their best foot forward. Prospects will be shown how they will be used in the scheme, shown what life would be like on campus, go to a game (like MBB or another sport that may have a nice turnout), hang with current players, meet with the academic team, etc. Official visits are paid for by the school.
Each school pushes whatever is their best selling points. SEC schools do their best to get prospects on campus during the season so they can attend home games and experience the environment. Pregame prep, walk to the stadium, sideline access, etc.