Resignation In Probation Period - Appoinment Letter

As i got an offer to further study, i have decided to quit my job, any way i am still in my probation period and not received any confirmation letter yet, will i need to get the relieving letter after i hand on the resignation letter? The company i work at is a very small company which we don't have HR department, so can anyone advice?
By the way, if the appoinment letter not stated anything regarding to resignation, is it still compulsory to give one month notice? or i can just give an immediate resignation letter will do? really need help and advice..i work almost 14 hours everyday without OT pay..:(

If the company is very smal you can directly talk to plant head or the owner of the company?
They can guide you!!!

well, i have talk to the owner of the company, she didn't said any notice required just let her know the effective date of resignation, she seems very unhappy with that and my colleague said she never give relieving letter. but i am wonder,what's the effect to me if i don't have the relieving letter? will it be a trouble when i want to apply a new job after my study?