When it is talking about Magic Situation Commands, it means the built up Situation options that present themselves when the Action Arrows are built from magic combinations. The only commands that matter would be: Blizzaja, Firaja, and Thundaja. Should you have built the action arrows up enough using these abilities, you'll see them pop up allowing you to use them. Just attack a few enemies to build up one arrow, then use magic to attack large groupings (or use on bosses like the Demon Tower or Demon Tide) to activate the situation magic options. This does not require Spellweaver or Finish to be executed, as they are used for another trophy: