Meditation is training / exercise for the mind. Theravada Buddhist meditation’s ultimate goal is to help you retrain how your mind thinks so that you can become free from suffering. To train yourself to change the type of thoughts you have, and be able to reduce and eventually stop having thoughts that cause you to suffer. As you become increasingly free of the suffering, caused by your mind, you will find yourself becoming increasingly happy, joyful, peaceful, and kind… both to yourself, and to those around you.
Thanissaro Bhikkhu - 20+ years of dhamma talks
Gil Fronsdal - 20+ years of dhamma talks
You can meditate and not believe in the supernatural. Gil Fronsdal describes what he calls natural Buddhism, which is also how I approach meditation. In this aspect, Theravada Buddhist meditation and Christianity are very different.
An online meditation manual will give you meditation instruction basics, and you can also download the manual in a variety of formats.
The random sutta link allows you to begin to explore the suttas (texts). I recommend eventually reading one a day, but only after you have gotten into the regular habit of listening to dhamma talks, and meditating every day.
If I can offer some initial advice; Reading the suttas too soon creates a danger, especially to intellectual types, of having meditation be an intellectual pursuit like the study of history or chemistry, rather than a skill like drumming or dancing. So stay away from too much reading in the beginning, and instead spend the majority of your time listening to the dhamma talks & meditating.