In the mood for which preposition 'at, in, on' should I use?

[Twilit1988]

Hi,

1 : ''I'm not in the mood for playing checker'' correct?

2 : ''Wish you were with me then we would go to the river i'd catch fish and you'd fry'' correct?

3 : ''I'm not in the school or at school''?

4 : ''I'm in the shop or at shop''?

5 : ''I'm at river'' correct?

6 : ''He will surely be happy'' or ''he'll be surely happy''?

7 : ''This is what'' has the same meaning as ''that's what'' has?

[Doca83]

And i ask this. I don't understand when I say at , in or on.

[Twilit1988]

Will i get the answer?