use of "the"

[English learner]

Can anyone explain the reason why "the" is used in some cases and not in others? I don't think the meaning of the sentence changes.
"People go skiing in the winter." "People go skiing in winter."
Is there a slight difference? I know British English doesn't use "the" when referring to being hospitalzed, "He is in hospital" instead of "He is in the hospital."
Am I wrong if I don't use "the" or if I use it??

[rewboss]

In the first example, there's almost no difference at all.

In the second, "the hospital" would be a definite hospital -- we use "the" to mean, "you know which hospital I am talking about". If you tell me that Jim is in the hospital, you assume that I know where to find him without having to ask any further questions. But if you simply say he is in hospital, it could be any hospital: the point is he is receiving hospital treatment.

[AELC]

I don't immediately feel any difference between using the with the seasons, or omitting it, but I'll think some more about it

I can tell you that when we use the with school, hospital, church, prison, university or college, we are referring to the place/building. We do not use the when we refer to participating in the activity/process of that place.

He goes to the school every day to deliver milk.
The governor inspected the prison.

She goes to school in New Jersey. (She's a student.)
He was in prison for two years. (He was a prisoner.)

Unlike British English, In American English we use [I]the[I] in both cases for the word hospital.