Chemistry - Polymers Topic

My specification says this:

recall the addition reactions of alkenes with the following: bromine to give a dibromo compound (and the use of this as a test for unsaturation), hydrogen bromide to give a bromo compound, hydrogen in the presence of a catalyst to give an alkane (Ni with heat and pressure or Pt at room temperature and pressure), water in the presence of a catalyst to give an alcohol (conc. H2SO4, then add water or steam/H3PO4/ heat and pressure)

However I don't completely understand the bolded parts, could someone please explain them to me?

Alright, an unsaturated hydrocarbon is one that can still have hydrogens added on. take ethene C2H4, it can be hydrogenated to ethane.

and H2SO4, and H3PO4 are catalysts that can be used

Thank you so much, that helped loads!
(+rep)