Tell me what difference is there

"If you were to win the lottery, what would you do?"

"If you should win the lottery, what would you do?"

Those both mean pretty much the same thing, although the second is more formal and sounds a little old-fashioned. Both refer to a possible future event.

Won is past tense.

"If you had won the lottery, what would you have done?"

(Note: I grew up in the USA, but I've lived most of my life in Britain, so my English is a weird amalgam of the two usages.)

A lot of English as a Second Language students get easily frustrated because there are several ways to say the same thing. Some are more correct than others but are still considered correct to add to the confusion. The first poster described it very well.

I can understand!!!!
Thank you for explaining in detail😄
I've always wanted to visit Britain,now I decide to visit!!
I'm finding you British guy is so kind😍😍

To win proposes a hypothetical scenario. Won refers to the past