A functional group is a reactive portion of a molecule. The combinations of functional groups with hydrocarbons produce a vast number of compounds. Particular types of reactions are associated with the functional groups with different structural attachments, giving rise to names associated with such compounds.
There are names associated with the functional groups themselves - a good collection of such groups with their names can be found in Wikipedia. A few examples are given below.
Organic molecules containing a hydroxyl group are known as alcohols. Hydroxyl wiki.
Note that the carbonyl group is the functional group involved with several of the hydrocarbon derivatives shown above. Carbonyl wiki.