Commas are used to separate one part of a sentence from another part of a sentence.
Commas do not always go with, or always not go with, any particular word. The perennial questions (Do you use a comma after however? after therefore? before and?) show a screaming ignorance about what commas are for. Commas can appear before or after any word in the language, if the sentence structure requires. They do not attach to words, but separate one part of a sentence from another part.
English has only four and a half occasions when you should use commas. When you don’t know whether to use a comma, simply hold up these rules and see if any one of them applies:
Rule 1. Use a comma with and, but, or, for, nor, so, yet to separate two complete sentences. ...