I have a confusions on grammatical error. Please help me.
When can I use “for us” and “to us”?
Depends upon the context as there is no hard and fast answer, especially when using vernacular slang. Typically “to” is direction/location and “for” is on behalf of.
For Example:
for us: She brought back a big box of chocolates FOR US.
to us: She gave a big box of chocolates TO US