I actually looked it up and it makes sense! You don't use 'the' when when referring to the place as an institution where its main function happens (e.g., learning at school or university). 2. Use "the" when referring to a specific building or when talking about a service being used as a physical place (e.g., going to the bank or to a particular hospital).

It’s clear from your question that you understand (better than some of the answerers!) when to use ‘the’ from the way you have posed your questions. Two things to point out. ‘Going to hospital’ and ‘going to university’ are Britishisms. Americans ‘go to the hospital’ whether you are a patient or an employee. Americans go to ‘the university’ but can go to ‘college’ (as a student somewhere) or ‘to the college’ as a professor (a specific college you know about)

#1 It's your choice. You are free to use "the" or not use it. However, your choice is not a random one. You should choose based upon the meaning you wish to express. Here's a simple test that might help you decide. Ask yourself if the sentence would make good sense if another specifier were used. Does saying "her school", "this school", or "that school" help to clarify the meaning? If so, using "the" might be a good choice. Pay no attention to people who tell you which choice is the most common one. Your choice should reflect your own thinking. You should not care what words are most often used. The choice has nothing to do with whether she is a teacher or he is a priest. Some examples: BETTER TO USE "THE": A: Will she go to the grocery store tomorrow? B: She will go to the school. ("The" helps because it accentuates the difference between "the grocery store" and "the school". Notice that it would also sound good to say "she will go to her school".) BETTER TO OMIT "THE": A: Is Tommy still going to school? B: No, he is in college now. ("The" would not help because there is no focus on a particular school. Notice that it would not help to ask if he is going to "his school". It doesn't matter which school. The question is whether he is a school boy or not.)

I am not a native speaker but I'll try my best to explain how I think it's correct! 1) In the sentences you provided you shouldn't use 'the'. But for example 'I'm going to the bank tomorrow', then you do use 'the'. 2) You're correct about this! If you're 'in' daycare/nursery etc. it means you're enrolled. If you're 'at' a place you're there right now. 3) The first sentence makes more sense. 4) "I saw your mom/mum in the hospital". This is another example where you do use 'the'. I'm honestly not sure what the reason is for using 'the' sometimes but not the other times.