On PS! Most people set up a bracket using challonge.com
Announce your tournament in the main chat (but remember not to spam it please). Include details and use appropriate formatting, meaning bold and not CAPS and tell people to PM you to enter. Put their names in the bracket, good to go.
In the future, simple questions like these can probably be addressed to a friendly staff member via a PM on Pokemon Showdown itself (you'll get a faster reply for sure.)
EDIT: To clarify I mean all the PS staff members are friendly, not that you should specifically PM a nice one :]