Is User Guide really necessary

Firstly please help me understand what guide truely means with respect to this link.
Secondly I had read that guide is an important part of a great UX, also by the answer of jensgram over here, it makes sense having such guides.
So as a UX designer,my dilemma is should i add guide on my app or just let the users discover its features?

PS: there is a FAQ page on the website, and the product will be used by users of all age groups and even by non tech savy people.