To help you set up your Goals, Calendar will ask you a few questions and then help you find open time on your calendar to schedule it. If you have a conflict come up with your Goal, it will automatically reschedule. You can also defer a goal at any time. Goals are meant to learn how to help you keep your goals. The more you use it - edit your goals, complete your goals, etc. Calendar will help find better times to schedule your goals in the future.
Here's a quick animation from Google's announcement yesterday:
Head over to the Google update blog to learn more or simply open your calendar app and start setting your goals today!