There's a great book by Culadasa: The mind illuminated. It covers a lot of what ancient meditators thought about the practice, but the essentials can be found in the first chapter.
Second this. He is a professor for neuroscience and meditation teacher for decades. Breaks it down into 10 steps, in plain english. A must, if you are into meditation, IMHO.
Not who you asked, but Healthy Gamer GG has a lot of short meditations that only take a few minutes. There's a course on his site but a lot of the same information is scattered throughout his YouTube.