Basically Ahrefs teach Us  How the website or blog should rank ..on google and gain 100k montly visitors 

Facebook Offer the blue print Courses in this you know about all digital marketing like app promotion ,ads management ,stories etc 

In google digital garage you learn lots of stuffs like digital marketing , coding ,machine learning and big data etc and its also offers the certificate 

As we know the udemy offers the different course for free and paid but in this stuff this premium SEO course are getting free of Cost