I've participated in and also run some group games, and I understand that overwhelmed feeling you have. The nice thing is...group games are not as complicated as many think! Many individuals feel like they wouldn't do well, but in my experience, new people trying out groups is a great thing! They are pretty easy to adapt to once you jump in. Groups are, in a way, just an extension of 1x1 games. You can do a lot of what you can do in a 1x1 game, really, and your experiences in 1x1 games will help you! Groups simply give you more opportunity to interact with more people, and a Game Master will control and mediate the setting.
The first thing to do: find a group that really catches your imagination.
Once you do that, look at what all they are asking you to read! If it is a system game, make sure you have access to the rules or books you need! If it is freeform, check to see if there only an interest check, or do they have a World Building thread you can peruse to get a good feel for the world they've made? One of the best ways to contribute in a positive way to a group game is to really understand the setting and story in the manner the GM wants you to understand it.
Secondly: The GM isn't just the person running the game. They are a resource, a guide if you need help or advice. Do not be afraid to ask a GM questions! If there's a lot of information to take in about their game but you are still really interested, ask the GM what the most important parts are to read for a new player and what can wait for later, if that's an option. That way, you can try to get all the information you need without getting overwhelmed by the amount, if there's a lot. Oftentimes, a GM running a group or recruiting for a group is typically happy to answer questions! So if you are unsure of a character concept, what posting speed they'd like, how to set up scenes for your character in their game, either PM them to run the concept by them or ask in their interest check. Another good idea, if you're very new to groups, is to wait to see how others are writing up their characters to get an idea of how to contribute in a way that meshes with others and adds to the setting.
So...how to "add to the experience/pleasure of the game"?
Group games have life breathed into them by players who plot and brainstorm interactions and scenes between their characters. If someone else's character looks interesting and you have an idea for a good scene between your characters, message that player (and include the GM in that message so they know what's up) to see if it would work. What groups bring is a more social, varied, and somewhat more energetic experience than 1x1s, although that's a personal experience of mine and not any sort of objective statement.
....I've...uh...probably rambled on at you enough. ^^; I hope some of this was helpful in some way, although you have my apologies if it was not.