Look around you. Every day, in every situation imaginable, there are hundreds of ways to meet people. There really are. You could strike up a conversation with a stranger on a subway. You could ask for some advice from the girl ahead of you in line at the supermarket. You could ask your coworkers to hang out, or join them for lunch. You could go to meetup groups, or meet people online and transition to real-world encounters. Point is, "How do I meet people?" is the most commonly asked question -- and it's usually the wrong one.
If you're a true introvert, your biggest enemy is yourself. It's your desire to be alone. It's your preference for living by yourself, for quiet moments away from others, for nights spent at home, watching Netflix or playing games. Making friends means making an effort to hang out with them, even when it doesn't seem like the most immediately pleasurable, comfortable, or convenient thing to do at any given moment.
I hate making plans. But once I'm in mid-plan with a friend or two, I have a great time. And yet, somehow I never seem to put two and two together. I tend to decline or avoid a lot of social plans. I'm sabotaging my own friendships when I do that. Friendships are like pets; they need to be fed, walked, and watered. Some of your friends will be super outgoing, and they'll do most of the work for you. But some of your friends won't; they'll be the passive party and expect you to make the plans. And either type of friend will occasionally, if not often, expect you to make the plans. That's what happens in a mutual friendship.
So I'd ask you to ask yourself: is your problem really about meeting people, or is it about staying engaged with people? If it's about meeting people (shyness), there is plenty of good advice on this thread about how to do it. If it's about spending time with people (introversion), that's going to require some regular, concerted effort to battle against your own inclinations. Sort of like battling the urge to procrastinate. You'll have to battle the urge to self-isolate. You'll want to focus less on the initial "ugh" factor in making or anticipating plans, and more on the fun you'll be having when you're hanging out.
Friendships don't just click into place on the first interaction between two or more people. They depend on proximity and frequency. They take time to develop, and once they've developed, they need to be maintained. They are conditional, and you need to live up to whatever the conditions may be in any given relationship. You're not going to ask a coworker to lunch and become friends at the end of that meal. You're going to ask that same coworker to lunch a second time, and eventually a third. And maybe you'll be friends at the end of the fourth meal.