can anyone explain to me what does this sentence mean (grammatically) ?
Literally “How it goes to you?” How are you getting on? How are you? Dir is dative, something like “to you”.
Ftornay hit it; would just like to add, an answer to the question “Wie geht es dir?” could be, “Mir geht es gut.” Or, “Mir geht es schlecht.”
Respectively and very literally that translates,
“To me goes it good” or, “To me goes it bad.”
Directly translating German into English can be very confusing - but if you do a literal translation, then think about what the one to one word comparion might mean.
The use of the dative is very common in German: an English speaker would say, “I am sick”, but in German one says,
“Mir ist schlecht” - "To me is bad, " or “Es geht mir schlecht” - “It goes to me bad.”
Each language has its peculiarities - German is full of dative use, which to English speakers (at least) takes some getting used to…