What is the concrete goal of a meditating session?

I started practicing meditation (I am a beginner), and I struggle to understand what the exact goal of the session is. In case it helps: my current goal is mainly to remove some stress/anxiety (I am not doing it for spiritual purpose but mainly for the practical implications it can have on well-being). In the beginner books I am reading, it is explained two things: 1. You should focus on your body's sensation 2. Whenever a thought arrives, you should acknowledge it, but let it go away to focus again on your body. What I struggle with is that I don't differenciate what is the goal from the tools/tricks we can use to reach it. In particular: is focusing on your body's sensation the actual goal? Or is it a trick used to get to the goal? For instance, it could be that the goal is not to focus on the body's sensation, but rather to not let a thought occupy the mind. In this case, focusing on the body's sensation is a trick we use so that we avoid a thought to occupy the mind (because we focus on what we feel). Overall: what is the actual concrete goal of the session. If it exists, I would appreciate an answer based on scientific studies (if they exist) that explain how exactly the session should be done so that it provides the best benefits.