Aromatic compounds consists of the compounds which include Benzene, and  rings of Benzene.
For eg,
Benzene, Toluene, etc...
Aliphatic hydro carbons consists of the elements - carbon, and hydro only, as in the aromatic hydro carbons; but the difference between them is, aliphatic hydrocarbons are those linear chain compound, and they doesn't include Benzene, or Benzene rings.
The alkanes, alkenes, and alkynes are all constitutes the aliphatic compounds, with the presence of some functional groups, or without the presence of them.

Hope this will help you.