Hrdrogenation is a process to obtain saturated hydrocarbons from unsaturated hydrocarbons.

See a common example :-
CH_2=CH_2 + H_2 (Pd)--\ \textgreater \  CH_3CH_3

The unsaturated hydrocarbon ethene is reduced to ethane.

The conditions require pressure (different for different reactions) and catalyst such as Ni, Pd, Pt...

The Physical properties might change as follows :-
(i) Unsaturated hydrocarbons are mainly insoluble in water but saturated are soluble. Therefore the insoluble becomes soluble .
(ii) The boiling point and freezing point changes as accordance to the compounds.

Hydrogenation is the process to change saturated carbon compound from unsaturated carbon compound.
R         R                   H   H
   C=C    ---------->  R C-C R  [AT THE PRESENCE OF HYDROGEN AND 
R        R                     R  R       catalyst of nickel]