In my experience you make friends with people when you share something in common. I met my best friend in high school. I was a scrawny 90lb freshman who was fascinated with computers. I found out that I could skip study hall by asking my teachers for a library pass. Every day I would ask for a library pass to go to the library where I could play with computer (an Apple IIe).
It just so happened there was another guy who did the same thing, so I was competing with him to see who could make it to the computer first when the bell rang. Whoever got to the computer first got to play, and the other person had to sit there and watch.
The other guy's name was John. We bonded over our fascination with computers, and became good friends. We started getting together outside of high school and to this day we're still friends. We just had a cookout at a local park a week or so ago.
In my junior and senior years I met two people at vocational school who shared my sense of humor. Those friendships would extend beyond high school. After we graduated, I would get together with them pretty much every weekend.
It was through one of these friends that I met several other friends, through activities, and started to get together with each of them, both together and separately. It was a nice group of friends.
And then one of them met a guy at work who was recruiting for a competitive team. He being the captain. We got together one weekend to learn about the sport, and that became a years-long hobby that would bring more friends.
These are just some of my own life experiences. I never went out looking, I stumbled upon them, and I've had some really great experiences just hanging out with friends and doing things we enjoy together.
Explore your hobbies and interests, and by doing so, putting yourself out there to meet others, you will meet people who share your interests, and will make friends. It can be online, it can be in person, it doesn't matter, you will make friends if you take the initiative to be where you can meet people. It might be a local book club, or an online community. Start talking to people and sharing your interests, and the next thing you know you have friends to talk to and do things with, and your friendship pool will grow.
Friends are people who share at least one or more things in common with you. The more you have in common, the more you will get together and do things. Just because a person only has one thing in common with you doesn't make them any less of a friend, it just means you both have other different interests, and so you may not get together with them as much.
I've met people when I least expect it. I'll be out doing something I enjoy, like a hike in a state park, and stop and talk to someone. You just never know when you'll meet someone who will become your next friend.
These days we tend to isolate ourselves, but you can't do that, you have to put yourself out there by doing/exploring your interests in places where people gather, whether online or in person.