Let's make some stuff clear:
Chinese is split into what's written and what's spoken.
The two ways to write are Simplified and Traditional. Mainland China will nearly always use Simplified.
There are a multitude of Chinese dialects but all of them will be written in the two aforementioned options. The two most well-known dialects are Mandarin and Cantonese. As far as I can tell from wiki's article on "Mandarin Chinese" and "Standard Chinese", Mandarin Chinese is just an umbrella term for all the different accents associated with Mandarin and Standard Chinese just refers to the official, "right" way to speak Mandarin. My bet is that whatever website that actually teaches Mandarin will already be teaching the "proper" way.
Mandarin:
https://www.youtube.com/watch?v=l7PiYBfaZUICantonese:
https://www.youtube.com/watch?v=6tCmGLjBqfAtldr: learn to write simplified chinese and learn to speak the type of mandarin chinese you hear from a beijing news reporter
