The Audience setting lets you decide what visitors you want to target in your experiment. In other words, on what page your experiment should be run and for who.
Audience is set up by one or multiple statements that need to be fulfilled by the visitor for him/her to be exposed to the experiment. This also decides when your experiment should run (E.g. when your A/B test changes should be executed)
The Goal setting lets you decide what KPI's you want to track in your experiment and has the same logic as the audience settings. In other words, what you want to measure that states if the test is a success or not. For example, completed orders if you run an e-commerce or click on a submit button if you have a content-based website.