If you own a long option position, and the option expires in-the-money, Collective2 will automatically exercise your position on the Saturday morning after expiration. This means you will buy or sell the underlying stock. Thus it's important that you have the margin available in your account; otherwise, you'll be greeted on Monday morning with a simulated margin call.
Similarly, if you are short an option, and the option expires in-the-money, Collective2 will automatically exercise your option. This too will mean that you will buy or sell the underlying at the strike price.
If you don't want to be exercised/assigned, then be sure to close out your option position before the end of trading on expiration day.