This is a tactics trainer that combines conventional tactics with guess-the-move puzzles. Sometimes there is a tactic on the board that you have to find, but sometimes there is no tactic and you just need to find a strong move.
Best use: if you have an annotated game and you want to struggle with the positions yourself before reviewing the annotator's comments. Load in the PGN and record your thought process at each step before moving forward (you can also graph the candidate moves you calculate). Then you can go back and review the annotator's comments and see the difference between your thought process and the master's thought process.
The "Save As" button lets you export your session so you can load it in at a later time using the "Choose File" button.