Unlike semantics, which are words with meaning, pragmatics are words which do something within a sentence. They change the meaning of the other words, or provide context, or establish the tone.
If I were to say that “the Earth is spherical” this is a factual sentence in which each word has a semantic meaning. However, if I were to say “well, the Earth is spherical” the word “well” is pragmatic and is doing the work of providing context. With this statement I am perhaps gently trying to correct a misinterpretation and offer relevant information to make the counterpoint.