If you go to the main menu it should have the controls in the settings if not when you start a race it tells you the controls in the loading screen just take a picture of them. Singleplayer is where you can find the episodes to start playing through an episode just click on the episode and hit start scene (or something like that). Splitscreen is just multiplayer so you can play with your friends. This game doesn't have online pvp (player vs player).
The challenges in the scenes in singleplayer change throughout each scene (ex: you will race against Hammond in one scene than in the next scene you will be taking a picture of a turkey.) Some of these challenges can be difficult so take your time. If you don't know what button to hit during some of the scenes it will tell you which button you need to use somewhere on the screen.
In Splitscreen you are just racing against ai or your friends. If you hit a silver balloon than you will get an ability which can be used to slow down your opponents or to give yourself an advantage over them. Also when starting the race, in the loading screen look towards the bottom of the screen and it will give you helpful tips.
Tips: The drift button can help you get around tight corners without hitting the brakes as hard. Trial and error is a big thing to learn from in the Singleplayer scenes so be patient. Use racing lines like an F1 driver (ex: go wide on the straight before turning sharply into a tight corner.)
Here is a photo of the ps4 controls if you're playing on xbox the buttons are in the same places as they are in this photo. Hopefully some of this will help you start out. This game is very easy to get use to after 10-20 minutes of playing through singleplayer.