Can black holes be used as an energy source I’ve heard that black hole will be rotating continuously which stores a huge amount of energy in its rotation. Will this energy be accessible, since the rotation is imposed on the space outside the hole.
What you are thinking of is called the Penrose process - a means of extracting rotational energy from a black hole.

The basic idea is that you allow a composite body to fall towards a rotating black hole. Once it reaches the ergosphere - that region, outside the event horizon, where the "frame dragging" due to the rotating spacetime is so severe that no body can remain stationary from the point of view of a distant observer - the body should split. One half falls into the black hole and the other orbits and flies out again. If things are arranged correctly then the returning part of the body can have a kinetic energy that exceeds the rest mass energy of the half that has fallen into the black hole. The energy comes at the expense of slowing the rotation of the black hole.

The Penrose Process (from Brito et al. 2015)


If the rotating black hole has an accretion disc (as many do if they are in binary systems - that's how they are identified) then another method is the Blandford-Znajek process. This may actually be the way that quasars and many of the energetic phenomena in gamma ray bursts and black hole binary systems are powered. In simple terms, a magnetic field that threads the accretion disc can be twisted up by the ergosphere. Material can then be propelled in jets along the rotation axis, but is given a spin by the field lines, which extracts angular momentum (and rotational energy) from the black hole. This energy can then be released when these jets run into other things.