Remember how video games used to include manuals inside the box? Nowadays, you'll generally find a little slip of paper warning you about seizures and a link to a PDF on a publisher's website. But at least Rockstar Games has an excuse if your copy of Grand Theft Auto 5 doesn't include an instruction booklet with the game--it's over a hundred pages long.
As such, you'll be able to download The Manual app on the App Store. The official app goes over things like controls and game features, but also gives you an idea of some of the activities you can partake in with the game. There's also an interactive version of the game map you can zoom in and explore, which should come in handy.
Although the iOS version is available now, Android and Windows Phone owners will have to wait a little bit longer. The app will also be coming to PC and Mac--even if the game isn't.