With goals you can determine whether your visitors have performed certain actions on your website. This can be clicking on a certain button, reaching a thank you page, buying a product, signing up for a newsletter and much more.
Once you have defined an action, it appears as a goal in the list of goals and you can see how many individual users have performed the action and how often the action was performed in total. You will also see Conversion Rate (CR). This number is the percentage of how many of your total website visitors performed the defined action.