There are a couple of things about
@texasvandy's example here that are not quite right, so I'd like to rectify:
There is no "switching or swapping" happening automatically after Match Day at all.
You will come out of Match Day with 1 Match school or Zero Match schools.
(If you have had any prematch offers, you
WILL have 1 Match school. If you have had interviews but got no prematch offers, you can still get 1 Match school on Match Day, or you can get the message "No Match").
If you have a Match school, but later on get an offer from a Wait List (as in the Feb and April examples given)
you will personally consider whether to accept that WL offer, or stick with your Match school. You must inform the WL school if you say "no". You must inform BOTH schools if you decide to say "yes" to the WL offer and drop your spot at the former Match school.
Yes, it's complicated. There are videos about it on TMDSAS and/or Texas Health Education Service web pages. I suggest you all read & watch them