In essence, abstraction means that one can treat problems in a way that are more convenient for the human brain to process, rather than in a ways that are more convenient for a processor of the Von Neumann type to process.

Two different structures might have members that are named, for example, "airflow". The variable, "airflow", will have different overall effects for a construct dealing with "carburetors"" than it will for a construct dealing with "simple fan".

C obviously presents the occasion for dealing with abstractions.