It's from the Mahabharata. And, yes we can get the required translation from the Kamakoti.org website. There you will also find the context in which it was said in the Anushashana Parva of Mahabharata. Also, it gives the details of the Rishi and other Nyasa details associated with the Stotram etc..
The Stotram that you linked in question starts with -
Visit What are some online sources to get unabridged Hindu Scriptures or to learn Hinduism? to find and read scriptures.
You can easily read/find Vedas in original Sanskrit at Sanskrit Wikisource, Vedic Reserve site, Snskrit web etc. sources.
Yes, the mantras you quoted is known as Shiva Sankalpa Sukta or sometimes "Shiva Sankalpa Upanishad".
Brahman is an ABSTRACT thing.
The Veda, Upanishads, etc, described Brahman in many ways. Lengthy discourses were recorded on this subject.
Mahavakyas will describe in a nutshell about Brahman.
The Mahavakyas (sing.: mahāvākyam, महावाक्यम्; plural: mahāvākyāni, महावाक्यानि) are "The Great Sayings" of the Upanishads, as characterized by the Advaita ...