This site publishes the Mahāsatipaṭṭhāna Sutta — the Buddha’s most detailed instruction on what to attend to and how — together with a short primer on his life and teaching.
The discourse
The text is Bhikkhu Sujato’s translation of Dīgha Nikāya 22, from SuttaCentral, dedicated to the public domain under CC0. The Pali alongside it is the Mahāsaṅgīti edition, also CC0. Neither carries any condition on reuse, and both may be copied from here freely.
The same discourse survives in a near-identical shorter form as Majjhima Nikāya 10. Where the two differ, the longer version expands the section on the four noble truths.
The primer
The Buddha section is a compilation drawn from introductory works on Buddhism, listed in full on its Sources page. It is a primer, not a scholarly edition. Where a page there and the discourse disagree, the discourse is the authority.
Practice
This site publishes the text. It does not teach the technique and gives no instruction in it — see Vipassana courses for where that is taught.