New to this - what is seo platform?

Usually means an all-in-one paid tool like Semrush, Ahrefs or Moz: keyword research, rank tracking, backlink data, site audits and competitor research in one place. Big agencies use enterprise ones like Conductor or BrightEdge. If you're just starting, you don't need one yet. Search Console is free and covers your own site properly. Get the paid stuff when you need competitor data.