An online course ... with or without a certificate of completion ... is, simply, education.   Some pretty smart folks create a path for you to follow, and they put into it what they think will be helpful to a n00b1e.   (Meanwhile, Tim O’Reilly puts into it what he thinks will sell it!   Natcherly.)

Does it “certify” anything?   I doubt.   The only way to build a house is to build a lot of houses.   But, it is perfectly legitimate to take a course in home construction at your local community college if that works for you as a means of beginning to learn the trade.   Take the course, but don’t immediately thereafter hang out your shingle, “Camel Construction Company, Ltd.”