I hated duty instances at first (and still kind of do when I'm forced to play with randoms and not FC mates). I was under the impression that everything could be done solo as many people seemed to tout but this was not the case. My first class was WHM so the pressure was much higher since the entire party relied on my ability to heal and stay alive, not to mention learn how to play at the same time. It wasn't easy and I admit I made a lot of errors along the way. But you play with people around the world and you will never see them again most probably, and most people understand what "New player dungeon bonus" means and will pick up your slack or even give advice when needed. Some mentors are absolutely hateful though, but you can always report them. Maybe you might not want to join an FC immediately and feel like there's a huge burden like some other MMOs put on you when you join one but don't worry, as long as you join a FC that has the casual tag in the recruitment page, you're golden. You will grow and likely become more social over time.

There are a lot of game mechanics to learn but they are all pretty much the same from dungeon to dungeon. Learn what they mean from a youtube video and just adapt and improvise. Until you reach savage content you probably won't need to look up boss mechanics and can enter blind as I have. The party might wipe once or twice for the difficult ones but it's part of the experience of becoming better. If you solely rely on guides all the time, you won't learn to adapt as well.

You can use party finder, which is a wonderful tool not very well known to new players. Say you are a new player in the title and people will join fully understanding of the situation. Try different classes too to get a better understanding of roles. Like WHM is DPS primary and heals secondary, which is contrary to what you would expect. These kinds of insights will help you play your main role better as you come to synchronize with party members.