Depression dementia. What is the remedy?

Hello doctor I wanted to ask you question. I am 26 years old. Doctor I think too much.. Over thinking over analysis of everything it's natural.. I am percusing my course from Russia. When I reach there m brain stops working. I get confused as in hostel many community ppl r there. There language is different.. I get puzzled easily.. there we have to take decision instantly. Have slow thinking. m 26 but my brain is like childish.. I take tension too much n I forget things there.. depression kind of...seeing people over there feel inferior very much.. I don't understand things easily.. Someone has to tell me in detail then I understand.. Tension.. Like a 26 years child brain is developed mine is not.. Doctor what is the remedy??