essentially its the same for a pc.
Download the league file into your saved games folder, start ootp, load the league, check for an updated league file, manage the team and export.
The hardest part and biggest difference with a mac is
finding the saved games folder. It's hidden by any Mac OS past Lion.
Check out this thread for finding your saved games folder:
http://www.ootpdevelopments.com/boar...databases.html