A normal starting point for developing a thesis about a topic is to narrow the topic into something manageable. You cannot possibly talk about every cultural effect of globalization in every aspect of the lives of people in every country in the world; such a project would occupy several lifetimes rather than a single semester. This means that you should choose a single region and a single cultural area.
For example, if you are interested in food, you could look at how globalization has effected the human diet, and especially whether the dietary changes in particular countries resulting from globalization have been beneficial or harmful to the health of local residents. Often the new diets, which might include fast food, are less healthy than traditional diets, but globalized food chains can also prevent or ameliorate famines.
Another possible area you could study would be a genre that fuses western and local cultural traditions, such as the Indian film industry (Bollywood) or South Korean video gaming. You could then look at the specific effects of these genres on the local cultures.
To find reliable sources, you could search for articles about your topic on Google Scholar, a version of Google that only searches reputable sources such as peer-reviewed journals. Another excellent starting point for research is the scholarly databases available at your university library website. Most university libraries have reference librarians available to help students learn how to do research; many also offer short workshops on doing research for university-level papers.