as From the Explore Tab, enter the edit mode by the orange pencil. Now select the Define tab to display the video keywords.

as To create a new keyword, look for the tag with the yellow star.

Note that the orange lock will serve to mandate those keywords upon upload. The publisher simply chooses the pulldown options.

as For sub-category, highlight the word and then look for the new keyword button at the top.

The "T" button allows you to correct a keyword. Once corrected, the keyword will be corrected on the video as well and combine.