Now that I'm out of high school, making new friends hasn't been something that I sought out willingly (no offense to those I befriended after high school). Late in my senior year, I scored a job at the local movie theater, where I spend 85 percent of my time, so even after I graduated I was seeing mostly the same people four or five days out of the week. Honestly, the only friends I've made after graduation were somehow connected to my job. As an introvert, starting my first job with strangers was crazy intimidating and nerve racking, but it was all worth it from the people I've met.
Not opening up right away to coworkers is perfectly OK! Introverts have a harder time showing their true selves at first (or 30th) encounters. It takes time, because many introverts are watching their coworkers, carefully deciding who is fit to befriend. If you're lucky, you'll find another introvert doing the same thing, then you can bond while scoping out your coworkers.
Once you've picked out your "squad," establishing a basic friendship is the next step. Many introverts, like myself, try our best to avoid small talk, but sometimes it's necessary in order to transition into a deeper conversation. I've managed to survive small talk with then-potential friends that quickly turned to an in depth conversation, so if you're a newly "adulting" introvert, just know that you may have to suffer a minimal amount of small talk in order to make new friends. Sorry guys.
After a little suffering, small talk is skipped and deeper or more personal conversations take place to create a solid new friendship. Congratulations, you made a new friend without totally draining yourself! But then there's the issue of bonding outside of work. Introverts have a tendency to stray from bonding that includes planning (since you see coworkers on the clock, bonding at work is easy). Although planned outings can be fun, introverts don't usually like attending them on a regular basis. However, seeing friends outside of work is a nice change, even though it can seem like a necessary evil. I've found that having semi-regular outings with my coworkers built up my tolerance for how long I can stay energized around those people (I don't know about other introverts, but personally I can build tolerances for certain people).
I thought making friends would be much more difficult for the sole fact that I'm an introvert. I discovered I was wrong (for the most part). However, getting a stable job after high school, or joining any group, is an important step for an introvert to make friends as a young adult, especially after high school and college. Many of my closest friends are my coworkers. It might be a pain at first to have to suffer through small talk and planned outings, but trust me, the friendships you get out of it are well worth it.