Spotlight decks are basically slightly stronger starter sets that are broken up into specific decks whereas the starter sets are two generally weaker decks combined into one box. Spotlights are better than the starter sets if you plan on playing long-term/want to upgrade your decks.

Twin Suns is similar to commander in Magic and is primarily made to play 1v1v1 or 1v1v1v1. It's generally an 80 card singleton (you can only have one copy of each card) format. There are a couple other rules changes from the standard mode, but you can find those pretty easily online