Well, now that you know what Super Mushroom Kingdom Wars is, you should be ready to start your army. The current rules are still under question, as the wars right now are 'defining' the rules. Here are the current rules. They are outdated, however. Click here for articles that explain things such as champions.
Since you know how to play now, you can start your army. Sign up on the forum in the last link (The main page for the forum is also located on the front page) and go into '"Army Applications". Create a new topic with your army as your initial post. Once a mod approves it, you're ready to go!
Now that you're playing Super Mushroom Kingdom Wars, why don't you help us edit the wiki? At the top right of the screen is the button "Create an Account". Click it, and fill out the form. Once you have a Wikidot account, go to the front page and enter the password 'SMKW' in the module. Congratulations! You can now edit pages.
But before you get too excited, please read How to edit pages.