don't worry, hairui. just read those wikipedia articles and take it from there. follow the links to explanations of bilingualism, second language acquisition etc. they are a good introduction. everyone has to start somewhere and wikipedia is not a bad place.
i think you are chinese, aren't you? in that case, you will have to really watch out when talking about dialects/language in the chinese context because chinese national politics has its own reason for classing them as dialects (national cohesion) when linguists outside of china actually do not. after all, you probably want to make your thesis internationally accessible, don't you?