Semantics is the branch of linguistics that deals with the meanings of words and sentences.
Syntax refers to the rules for combining words into grammatically sensible sentences in a given language.
Pragmatics: Pragmatics is concerned with the use of language in social contexts and the ways people produce and comprehend meanings through language.
Morphemes are the smallest meaningful units of language. They can be whole words (like "a" or "run") or parts of words (like "-ed" which indicates past tense).