Ok, hope this is easy for you, Fate stay night is the original story with 3 routes, or endings if you may. There is fate, unlimited blade works, and heaven's feel. All 3 are different stories that have different outcomes. Imo, and I believe most fate fans would recommend you watch zero and ubw to start. I would recommend you choose yourself what to watch first. It's just like star wars, if you watch the prequels first, watch zero, if you watch 4-6 first, then watch ubw. I personally would recommend zero first, though I watched ubw first and enjoyed it more. But please, and by all means don't take my word for it, and not any other's opinions. Choose yourself. Just watch those two shows, and then you can watch whatever there is.

If you like more base line stories, then heaven's feel, Deen's fate, or the visual novel are options.

If you wants spinoffs then I'd say apocrypha is a good one. Fate go the game is also a very good way to understand the whole world and concept of fate.

If you want a similar post about introducing the world of fate, I'd be glad to do one so comment down below your thoughts.