Unpack the archive file:
tar -xzvf BianchiGP.sageworksheet.tar.gz
Then go to the folder that contains the unpacked files.
Load BianchiGP.sagews into SAGE.
Hit the key combination "Shift+Enter", and wait to get the message
"BianchiGP loaded into SAGE. Type "BianchiOrbifold?" for help (taking care not to indent this command)."