As for the signed data, it's the "message hash" (aka Z-value) which is the hash of the unsigned transaction with stripped parts depending on the "sighash type".
On that website, the whole process from unsigned raw transaction to signed raw transaction is explained here:
https://learnmeabitcoin.com/technical/keys/signature/#legacy-algorithm (example is for the commonly used "sighash_all")
Sighash type is explained just below that page.