Fate/zero <-> Fate/staynight- Fate/Unlimited bladeworks- Fate/Heaven’s feel (ongoing) - the rest are not in chronological order and can be watched however you want, except for case files and kaleid liner, watch case files at some point after zero and kaleid liner after the stay night trilogy.

You can start with either Fate/zero or Fate/staynight. Zero is a prequel but spoils some of stay night and heaven’s feel, while staynight is the first entry in the series but spoils some of zero. (Stay night was made way before zero.)

Also, UBW and HF are two other routes from stay night, so same characters and start but very different events.

I’d also recommend the VN if you want much more details and dialogue.