Usage means how words are used/accepted/understood.
Ex: When writers go wrong, it can be grammar, punctuation, usage, spelling, etc.
Ex: The non-word "alot" is in common use, but it is not proper usage.
Ex: "Ain't" is acceptable usage in some communities, verboten in others.
The nouns usage and use are related in origin and overlap to some extent in their definitions. Read more here
People frequently use usage when they should use use. The noun usage should not be substituted for use when the meaning is "the employment of" – even if you ... Read more here.
All the best.