If you use a real estate agent to sell your home, you probably won't meet your buyers until after the closing -- if then. Your agent (or the buyer's agent) will handle visits to the house by potential buyers and probably encourage you to make yourself scarce during those visits lest you blurt out something you regret later.
You may meet your buyers' real estate agents if they choose to formally present purchase offers to you and your agents. You may even be handed photos of the prospective buyers, and personal letters, if they're in a competitive bidding situation. And you can certainly find out their names from the purchase offer forms, in case you'd like to Google them later. But that's still not a personal meeting.
Even closings are often done separately, with you meeting with the escrow agent on one day to sign documents and the buyer doing so on another day.
It's not that there's any law against meeting the buyers -- but you'll probably appreciate, at various times along the way, having your agent serve as a buffer in any negotiations and be the bearer of bad news, if need be.
After the closing, however, arranging a time to meet with the buyers at your house can be a nice gesture -- and a good opportunity to show them things like how to turn on the furnace, turn off the security alarm, and which plants are weeds.