It is not always easy to separate fact from opinion. Skilled writers can make you think their interpretations are facts. Assumptions should be reasonable. Note errors or omissions. You should explore enough sources to obtain a variety of viewpoints.
Primary sources are the raw material of the research process.
Secondary sources are based on primary sources. If so, locate these sources for more information on your topic . Learning how to quickly determine the relevance and authority of a given resource for your research is one of the core skills of the research process. Since anyone can, and probably will, put anything on the Internet, it is necessary first to evaluate the material before using it for academic purposes. Because something appears in electronic form on the Internet, it is not inherently better material than what is found in print sources.