The difference between at and on.
At is very very close and beside, on is very very close and over or above.
You can be at a thing made of moe than one element. But not on it.
At the weekend not on it.
A list of some interesting prepositions in very short simple phrases containing the word open that help show some more preposition relationships.
Open to customers. (The car park space limits on who can get in.)
Open till the last minute. (This is when the shop shuts.)
Open for her (She can get in, a gap in time has been made)
Open to her (She can get in, a door has been made)
Open for the night (People can get in that night)
Open to the night (wide open space the whole night can get in)
Open along it’s edge (A description of the opening on the object)
Open for business (Open for an activity that takes time.)
Open for Christmas (Open for a time.)
Open in Newcastle (Newcsatle is a place we have an open shop)
Open it on the table (The table is the surface it must be opened on)
Open over Christmas (Open from time to time during the period.)
Open to new ideas (The ideas need space we will give it.)
Open to suggestions (Same relationship to suggestions)
Open for suggestions (I have some time for suggestions)
Open under pressure (There is a force opening this thing, pressure)
Open by law (The reason, law, forces it open)
Open due to popular demand (The reason, demand, asks for it to be open)
Open at the moment (The time is now, the state is open = at)
Open to the moment (Make space for the moment, allow it in)
Open from Monday. (Monday is when the shop starts to do business.)
Open part of Monday. (We are talking about how the shop opens on Monday)
Make your own rules.
It helps to think up youre own little rules for the things you notice about prepositions.
Here is one of mine.
Go is often followed by to. Remember Go -> to.
Here is what Wikipedia has to say.