2. What is meant by the term Protostar?
A protostar is a star which is glowing because of energy released by the gravitational infall of material (as opposed to nuclear reactions, which produce energy in the later stages of a star's life).
This photo of the Eagle Nebula taken by the Hubble Space Telescope gives an excellent view of the formation of new stars. The protostars can be seen forming amongst the columns of gas and dust.