I am super happy that you want to contribute to Brawl Time Ninja!
First, you are going to need a GitHub.com account. GitHub is the platform that hosts Brawl Time's source code. Signing up and contributing is free.
Next, you can use your account to sign in to the Brawl Time Ninja Content Manager: http://brawltime.ninja/admin
Under Collections, select the kind of article you want to edit. For example, to write Brawler descriptions, choose "Brawlers".
Select the Brawler or create a new entry if there is none. Fill the data, for example a Brawler attack description, or write your Guide.
When you are done, click "Save". When you are done, set the status to "In Review". Shortly after your changes have been accepted, they will be available on the website. Cool!