When coworkers say “stay in touch” what does that look like?

I’ve always leaned on the side of keeping my work life separate, so I have never had any lasting relationships with anyone I worked with. This is something I want to change somewhat but I don’t understand what I’m supposed to say to someone who’s left the company. Do I just email them every several months and ask how things are? That feels very forced and unnecessary to me, and almost like I’m doing so just for potential job connections