When I first started learning about punctuation, I found out that you should always have commas after words such as "today," "sometimes," "yesterday," and so on. Today, I found a website that disagrees, it says:
If you have an introductory word (or two) that is being used as an adverb (usually answers the question of when, where, why, or to what degree), then no comma. If it’s being used as a conjunction, then go ahead and use a comma.
“Someday, I’d like to go on a cruise.” — This is incorrect. Someday is functioning as an adverbial phrase, answering the question of WHEN I would like to go on a cruise. Correct would be this:
“Someday I’d like to go on a cruise.”
I want to know how legitimate this website actually is. Can someone verify this for me?