New Player Help?

I want to join a game on here, but I'm completely new to tabletop role-playing games like D&D. Should I join without knowing about how to play, or should I learn first? Where do I find the rule book to read if I have to learn that way first? I really want to try this as it looks fun but I don't want to join a game and be "that player" that doesn't know anything.

It's a good idea to have at least a marginal understanding of the system you want to play, and some systems have free rules available like  DnD 5e basic rules or  Pathfinder SRD as you mentioned D&D as an example. Many systems sell pdfs on the web, and youtube also contains introduction videos to many systems. Searching for games open to beginners/newcomers/new players is a good idea, whatever system you are wanting to play. If you find a game that conceptually interests you, you can look up info about the system to see if it sounds in your taste. Also check out the  Roll20 tutorial to get familiar with the basics of the platform.

Andreas' advice is spot on, I'd also suggest patience. It can take a while to find a game (simple supply and demand given the player to DM ratio) and even longer to find the right group for you... all of that aside though, it's worth the wait and you can always use that downtime to follow Andreas' advice ;) Above all else though, welcome to Roll20!  This thread has some further tips for getting up and running.

I was that player a decade ago, still using the same character, remodeled from 3.5 to 5e, 5e is very simplistic, 4e & pathfinder are built for intricacies, it's supposed to be complex, that's the goal. 5e is good for new players because it's mostly "You are spawned in this new world, you have your Class picked, your background picked, and your Race picked, you sifted through your starting equipment, and now, here you are, here's the scene, what do you do?" because the point of and good game I've found is that it's the Players that add vibrancy and color to the Game's world, the GM might have all of the weird awkward characters and events planed, but if the player goes entirely off script, the cameraman follows the Player, not the Plot. Be your character, play if how you think your character should be played, find one that works for you. I'm a Shadow Sorceress myself, Wood Elf, left home at a physically mature age of 18, but, by Elvish standards, she's but a child for another 80 years, at least mentally. Being a Wood Elf, she left for good reason (Magic + Wood Elf = bad combo, lore-wise), and she was not alone, joined by her childhood companion of the same age, a Hexblade Pact Warlock (go figure, I managed to pick the only 2 innate Spellcasters that DON'T get Rituals by default! Sorcerer & Warlock) My first GM explained it to me quite easily, you should only build a character if you think you can actually play it. If you know tons about plants, Druid might be right up your Alley. Ores and Minerals and Metals more your thing? perhaps a Dwarven Cleric? Demons? Tiefling has your back. one with the shadows and holding everyone's wallet for ransom? Rogue my friend! Raging Berserker? or maybe perhaps just a fan of Grog from Critical Role? Goliath Barbarians are just the right fit for you. Geek and Sundry on YouTube has a Campaign called Critical Role which is actually GREAT for learning 5e, although, just a heads up, it is home brew, which means that it is custom content, lots of it at that, for example, their Bardic Inspiration offers 1d8 when the PHB says 1d6. I'm only on about episode 7 of Campaign 1 (which is actually their second Campaign, but they didn't think they'd get _THAT_ popular, so they didn't record the 1st one as well)

Oh, and it appears we have a nice article on our wiki that is perfect for this :  Introduction To Tabletop RPGs (and a crash-course on Roll20) I wonder why it isn't on the stickied  New to Roll20 or RPGs, or Just Need Guidance? Click Here! thread? Blue64 said: 5e is very simplistic, ... is good for new players I agree with this, and it having the largest community helps too.  Blue64 said: My first GM explained it to me quite easily, you should only build a character if you think you can actually play it. I don't agree with this. Sure, applying real life knowledge and personality can enhance role playing certain archetypes of characters, but it shouldn't really restrict what kind character you would play. But if you mean that one shouldn't play a character with tons of complex abilities and options one doesn't have any grasp of, then I agree partially. Full spellcasters like Wizard, Cleric and  Druid with their many spell choices and abilities could be a bit overwhelming for new players,potentially leading to constant rules-checking, spell-lookup, combat-choice-paralysis which could lead to less enjoyment of the game in itself. As part of playing rpgs are to explore and be someone else, so a shy introvert shouldn't  be discouraged to play a charismatic bard if he/she wants to.  The stats and abilities of the characters are there to simulate things the player is not, so the above example could in a social encounter simply say something along "my bard gives the barmaid a sly smile and compliments her, trying to get to know gossip about the city lord". The GM could well agree with this and have the bard roll for persuasion and then briefly describe the following events.  Same goes with knowledge rolls and similar. Blue64 said: Geek and Sundry on YouTube has a Campaign called Critical Role which is actually GREAT for learning 5e They are fun to watch and I guess you can get to know some of the tropes of D&D and some familiarity to 5e mechanics, but it can give a distorted view of ttrpgs with all the player being voice actors and all.

That's why I pointed out that the Campaign they're using is a Homebrew one, they also cover things like how to use the various Tools, such as a Tinkerer's Kit, which their Gunslinger Percy uses multiple times before even Episode 10 of Campaign 1. I still personally haven't seen anywhere other than an Unearthed Arcana Spell that actually references what Skill is paired with what Tool (not counting Thieves' Tools which is clearly a Dex Roll, like everything else for the Thief Archetype)