First, there is no set rules or you can say in some cases, there are some set rules for prepositions. You need to get some of them by heart.
e.g, on TV, on Sunday (any weekday), in January (any month) and so. these are set rules of preposition which you need to use at all cases. There are not exceptions to this.
In some cases, you need to use your discretion while judging your sentences. Now, try to get the meaning,
- on the table
- under the table
- at the table,
- over the table
Do they have different in sense and meaning? Yes they do and I am sure you have already known it.
Likewise, it will be always on the admin page.... (and not at the admin page..). On screen or TV or something like this, we use 'on'. You're navigating to a page and you are seeing it on your computer and hence, it will be on the page and so.. It implies, on this page, you will see it but at this page you can get it. Makes sense?
Likewise, you cannot say going on the room. It will mean something going over the room (closely). It was an action of a direction and hence, it will always be .. to the room But you need to say.. i am going on this page. In this case, this sentence means reading the page and no movement is involved here.
We use 'on' to be at a road. It's simple and get it by heart.
Hope this makes sense. Do ask me if you get more or if you need more clarification or if you have some more discussion on this.
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