How to use official documentation to figure out what namespace to use
I was able to discover the namespace by finding the documentation for the Term class here.

https://api.drupal.org/api/drupal/core%21modules%21taxonomy%21src%21Entity%21Term.php/class/Term/8.1.x

And on that page there's a namespace section that said Drupal\taxonomy\Entity so I used 

\Drupal\taxonomy\Entity\Term::create


and that worked.

So I believe in order to find the right namespace to use, you have to find the page for the class that is using the method. In this case Term. And then find the namespace section and put that before the class when you are using a method of it. 

(This might be obvious to everyone else, but it took me a bit to figure out)