They are completely disconnected, with the exception of the occasional spinoff or direct sequel, but those are easy to identify. The last game is probably the easier one of the series to pick up and play (this statement has been true for the whole existence of the series)

Where to start? Depends. Everyone of them is a huge game and a big time investment.

Taking into account you have no nostalgia for the series, I’d say your options, in order of what I think would stick are:

• Option 1: the last one. If you just want to play a modern action/rpg game with AAA sensibilities but weird enough, is not a bad option. You have no need for any previous knowledge, the gameplay is completely different to the one in previous entries, etc. Haven’t played so I do t know if it’s any good.
• Option 2: the 7 remake. One of the biggest milestones in the series retold for modern audiences, with updated graphics and narrative.
• Option 3: 16bit retro experience: FFVI, SNES or GBA version. The pinnacle of the formula for the 8 and 16 bit consoles. Upcoming titles in the series are way different. Great in every way a game can be good.
• Option 4: the 7 vanilla. The first international massive mainstream success for the series and one of the more influential video games in history. After this one, if you loved it:
  • Option 4a: the PSX trilogy. Go for FFVIII and FFIX for the full pre-render backgrounds and 3d models god killing trio.
  • Option 4b: the complication. If you are really into the setting and characters you have a few games complicating this one under the “Final Fantasy VII Compilation”. Some aren’t even RPGs.

If you go completely Final Fantasy insane after any of those, start with FF, the first one from the NES and make your way through them all. Prepare a couple thousand hours.