
Presents an introduction to meditation according to Buddhist principles, describing the advantages of the practice and addressing some of the difficulties that can come up.
A great starting point can be Shinzen Young's The Science of Enlightenment and/or Sam Harris's Waking Up.
After that, you might look into Why Buddhism is True or The Yoga Sutras of Patanjali or Mindfulness in Plain English.
The Healthy Gamer Youtube channel also has great videos going into this and how they tie into psychology.
David Chapman's https://meaningness.com/ is also pretty great.
They're both more like "how to" guides than spiritual, and mention Buddhism or other practices only in passing (both have much more explicitly spiritual material too for those who want that), and Fronsdal jokes about the "B-word".
What I get out of it varies, going from just 5-15 minutes of calm and relaxation to multi-hour deeper meditation, to tumultuous sessions where I get no calm but all kinds of issues or ideas force themselves to the surface. I feel I benefit from all of it, but it's a method or a tool for me, not spiritual.
The book Mindfulness in Plain English is a great introduction to mediation if you are curious.
But, a quick, short answer - meditation is like going to the gym for your brain. In meditation, you practice detaching from thoughts. A practical example: Let's say you have a rocky relationship with your boss or a colleague. Maybe they say something you perceive as a slight while grabbing a coffee in the morning. Instead of fixating on it all day and letting it disturb your work, you just let it go. Not attaching to our thoughts doesn't mean we can't focus very hard on things - in fact, letting your negative thoughts go is what is going to allow you to focus hard on your work the rest of the day!
(Also, there are many types of meditation, this is just one form of meditation... again, lots of nuance here that is hard to get across in this format.)