The usage argument is: save file_name.fasta, object, selection

Here is the example, using PD-1 PD-L2 complex 6UMT (assuming PyMOL object name is 6UMT).

• save all chains: save file_name.fasta (if you have more than 1 object, it will save all chains).
• save all chains from one object: save file_name.fasta, 6UMT
• save one chain from one object: save file_name_chainX.fasta, 6UMT and chain B
• save two chains from one object: save file_name_chainXY.fasta, 6UMT and chain A+B