How are people text messaging me and where do those messages go?

U.S. customer here. Lately, I've been getting text messages sent to our phone numbers. I don't remember setting this up and/or enabling it. 1) How do people get the impression they can text the number? 2) When they do text, where does the text go? I can't find them in the system anywhere! I only know I'm getting them because I get an email notification when one comes through.