It really is good advice, and you do get more and more energy to do it after you get started. The thing I did was DnD, and I just found people in the area advertising in-person campaigns and went to some. I only wanted to do a social day once every week or two, so I started with that. That didn't last long, though, since after finding the one campaign to be really fun, I ended up joining 2 more and having multiple sessions every week! I wouldn't have had the energy to start with that, but now I've got plenty. It's a bit of a balancing act to both acknowledge the height of the mountain you're about to climb, but also keep in mind that all you need to do right now is take a single step.

Just do it once. Then do it again. And again. Break the process down into the smallest steps you can think of, and just do a little every day. For example, today, type meetup.com in your browser and hit enter. If you want to do more, that is fine, but if that's all you can do, then accept that and go on with your day. Tomorrow, you can do the same thing, or you can try putting your location in the search bar. If even that is too much, you can just set a timer for 1 minute and think about searching for groups of people to meet. Or once you have some events that you might be interested in going to, and know where they are happening and that they are happening today, you could spend 1 minute thinking about walking out the door to go to that event.

Often what happens is that by just taking the smallest first step, you keep going. Because you feel rather silly "just" doing something for one minute. And sometimes you just do it for one minute, and that's all you can do, and that's okay too.