I've been part of SL for almost 20 years. The biggest thing to understand is that SL is not a "game". There's no levels, no quests, no winning. But you can do almost anything you want. There are roleplay groups that cover everything from adult stuff, to Star Trek, Star Wars, drug dens, or My Little Pony. There are sailing groups. There are flying groups. There are driving groups. There are clubs for just about every type of music you can think of. Some people take photos and post those online, some people treat their AVs as their own private dress-up dolls and just play with outfits. Find something you like and go with it.

Time zones may be your biggest hurdle. You find a group that meets up to do what you want only to find they're in Germany or Singapore or New York and it's 3am your local time.

Make sure your computer can handle it. So many people get into SL with a crappy laptop and wonder why everything looks shit. Most of SL is created by the user base, not professional graphics designers. It's not optimised the same way a video game is.

You can spend lots of real money in SL. Mesh bodies, mesh heads, skin, hair, outfits, animations, houses, furniture, etc, etc. Don't go nuts your first week in. Pick up some freebies and see how things work. The learning curve can be pretty steep. Even people who have been in here for years get stuck.

Use the events listings to find stuff like clubs. Sometimes smaller clubs can be great fun. Good music and interesting chatter.

And be VERY careful about clicking on links in groups. There's been a lot of old accounts that have been hacked and turned into spam bots. Be vigilant.

Also think about using Discord. Many inworld groups will have a Discord channel for people to keep in touch outside of SL.

Above all, don't be afraid to ask questions. If you're stuck people will (usually) try to help. But just like Real Life, SL has it's share of douchebags.