pragmatics:
The rules that govern and describe how language is used in different contexts and environments. For example, the words and tone of voice will be more formal when talking with the principal and may be very casual and include slang when talking with other children. Social rules are very subtle. Some children have difficulty figuring these rules out and applying them appropriately. As a result, they may be identified as having inappropriate or poor behaviour.
The aspect of speech having to do with rules of social interaction such as turn taking and staying on topic, as well as other socially acceptable interaction rules.
semantics:
The "meaning" of words, those connotations that you might look up in a dictionary (as opposed to syntax).
The use of language in meaningful referents, both in word and sentence structures.
The study of the meaning of language, including meaning at the word, sentence, and conversational level.