告诉你这两句错哪...

are you coming at august?   should be "on August" but not " at August"...

I am wandering where r u from?  "wandering" is wrong, should be "wondering"; also should be " I am wondering where you are from? " but not"....where r u from."

Even though I can understand people don't pay much attention to grammar in the daily non-formal writing, I personally don't like to use "r" for "are" or to use "u" for " you", just don't feel this is a respectful and decent way to write English.