You have 2 ways to reach the fees page : when you create the project or from the project's dashboard. Click here for more details.
From the fees dashboard, click on FEE CALCULATION METHOD drop down menu. Select COST BRACKETS.
Then OK on the pop up message.
Then click on MANAGE BRACKETS
Click on the "+" button
and enter the inferior-superior fee bracket, the fees percentage then SAVE.
CLOSE when you are done.
You have added fee brackets to your project !