I learned that Sun will be in Aries in May and Leo in August etc.,
Now when i looked at a chart of a person i saw Sun in Aries though the person is born in March, and his region is Malaysia.
Astrology is not a subject which you can learn in a day or two. It takes a whole lifetime to learn. The differences you found is due to different systems in astrology. First learn what is Ayanamsa which is there on the internet.