Vacuum should contain something in it. Because nothing is perfectly empty that's what I feel, but what is there left in it? Is there any matter or its just enegry. Can energy be pulled out of some space?
Vacuum is in fact not empty. According to our current understanding all of space is permeated by fields which due to quantum mechanical effects only tend around a zero energy value. This means that the vacuum is subject to fluctuations in the fields permeating it.
In essence particles pop into existence more or less randomly as a result of excitations in these fields making a vacuum a boiling sea.
The fluctuations are related to the Heisenberg uncertainty principle.
These fluctuations have been experimentally observed and are quite significant to modern physics. The Casimir effect describes the fluctuation in electromagnetic fields and has been observed in a lab environment.
An interesting article on quantum vacuum fluctuations can be found here: http://www.hep.caltech.edu/~phys199/lectures/lect5_6_cas.pdf
In quantum field theory, the vacuum is the state containing exactly zero particles anywhere in space and at all times. Since it is an eigenstate of the number operator, there is no uncertainty at all about this.
On the other hand, empty space between matter (i.e., what is informally called a vacuum) is never completely empty; it is still filled with the quantum fields emanating from the matter. Just like the space between the sun and the planets is not empty but filled with the gravitational field.
If this field is strong enough one can extract energy from it. For example, a ball falling in a conventional vacuum gains kinetic energy from the gravitational field.