Thers an online manual u can take a look. I think u can access it from the game main menu.
Dunno if it explains there but most of the icons in the lower part are to tell if some of the assists are on, like ABS, Traction Control, Counter Steer. Then thers indication for headlights, hazard lights, turn lights, hand brake. The acelerator bar in the right side, the brake bar in the left side, fuel level, tire conditions and track wetness level to know when normal tires will start losing grip. And some more im forgueting i think.