I would refrain from giving them any pointers or instructions in order to prevent imposing your own bias on their experience. When users can freely roam your application, you might find that they use it differently than you imagined.
Additionally, if you have the ability to observe the person while they are testing (which it sounds like in this case you do), pay attention to their body language. For example, if they frown a little or tilt their head after performing some action, it's likely that the result wasn't what they expected. Being present when this happens allows them to directly ask questions, which also can bring a lot of insight to you about the user experience of your app.
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