You earn it by completing many different actions, some as simple as drifting or driving at high speeds. This is the currency of Need for Speed Rivals. They might hate you for it, but it can be lots of fun travelling across the map trying to catch other people. If you're playing as the cops though, you are tasked with chasing the players down. If you are also a racer you can approach other players and have quick races with them, or help them lose the police. While online you can interact with the other racers in a few ways.
There is an option under the All Drive settings that allows you to play a private game and of course if you have no internet the game still works fine and you will just be playing solo. This can be good or bad, depending who you are with and the what you are currently trying to do. When racing around the map, you will sometimes come across other real world people, racing around the map in your game. Rivals is constantly connected to the internet. There are Collectibles you can drive through and pick up, and players will be able to activate any events they want by simply driving up to them. While driving around, you will see various other racers, some even being real people since the game is always online. Need for Speed Rivals is an open world game, with a large map that you can drive around freely in at any time.