This script use xcodebuild tool to build a Xcode workspace, and upload the ipa file to fir(https://fir.im/).
The usage of xcodebuild command you can see here: ManPages
You can point out your teamID, export type ... on the plist configuration file. More detail about the plist file you can see this：https://gist.github.com/phatblat/0dd175b406cf2f3fbfc9 or the man page above: ManPages