How do we can collect primary data on social research?

By asking people focused questions.

You first need a research question. What are you trying to discover and explain?
You then need a theoretical framework and a research design to answer your question, and then collect data that could help you to analyze and answer your question.
Data collection could depend upon your research design. Some research designs could include survey research, review of newspaper articles, and/or review of other cases that studied the same subject.

Just to clarify the difference between primary and secondary research:

primary data is freshly collected information gathered through questionnaires or focus groups that include questions designed to answer a specific question.

secondary research relies on information already available through secondary sources such as newspapers, previous research carried out, etc. that also help to answer the question (perhaps the same question if it's been asked before).