The main difference between primary and secondary sources is how you collect it. Primary sources is material you gather yourself, for example quotes from interviews that you conducted in person or quotes you have gotten directly via social media or email. Secondary sources on the other hand is something you have not gathered yourself, for example quotes from other articles, background information from social media or reports.
Primary sources are important because they are the essence of journalism. Without primary sources, no one would ever write something new but only copy each other. When you use primary sources in your articles, you introduce new points of view to the reader. Also, primary sources is more reliable than secondary sources. When using secondary sources, it is harder to check the facts and verify the information, and the risk of spreading false information is higher.
The best practice is to use a mix of both primary and secondary sources, but to try and keep secondary sources to a minimum. You should mostly use them as background information, and always make sure to get your own quotes and check the information before publishing.