Like the subject says, I'm new to all of this, and I'd just sort of like a quick ELI5 off all this, I've already applied for a game and whatnot, but I still have no clue how to "play" it.

How, exactly, to play, depends greatly on the exact game, and which rules system it utilizes.  At its most basic, however, roleplaying games are grandiose games of 'Let's Pretend', with one participant typically selected to be a storyteller/referee and provide you with the basic story, as well as have the final say on whether or not you succeed at what you're trying to do.  They describe stuff to the group, each player describes how their character responds (usually doing so in character...rather than saying, "I'll have Marko go check out the noise near the elevator shaft," it's "Marko checks out the elevator shaft," or "I'll check out the elevator shaft.")  Also, on here, most characters' actions are written out as if they were characters in a book, with the actions and dialogue appropriately fleshed out ("Marko heard the sound of a tool falling of a table, in the direction of the elevator, and paused from setting the explosives to go investigate, not wanting to be rudely interrupted by a security guard with a sidearm...")

There's more to it than that, of course...but that is the most basic essence of role-playing.

Some games are run using rules systems -- like Dungeons and Dragons, Savage Worlds, Fate, Shadowrun, Call of Cthulhu, Apocalypse World -- that define the character's attributes and skills. Most use some combination of dice rolls to determine whether an action succeeds.

Other games are run more freeform with few stated rules and  the character's success or failure in her/his actions decided, often entirely, by the Games Master (GM)'s decision.

Also, as a player, you'll usually create the character you play.  In freeform games, it's pretty easy.  Just describe the character, what they look like, their behavior and personality.  Choose a character portrait and write a character description, and you can start to play.

If you choose a game like Dungeons and Dragons or GURPS, you'll need to decide the character's stats, like how strong they are, and what specific skills they have.