recover a sum of money

Sir how to recover a sum of money from a person whom you just give as a loan or for the performance of a specific act which he fails to do so ,now want to recover money but having no written proof of all this dealing it’s all about oral dealing. But now this person not giving back my money ,what should do and what law will comes in motion .what kind of suit will have to file and which court criminal or civil and which provisions.