Vist their main page: http://wabbitemu.org/ for more information
Before we begin confirm you have download the above files
Select the last option, "Create a ROM image using open source software"
Click Next
Select "TI-84 Plus SE"
Click Next
Select "Browse for OS files on my Computer"
Navigate to where you saved "TI84Plus_OS255.8Xu" file and select this file. Click Open.
Click Finish
Pick a location and save your rom file.
TI84rom is a good file name