Textbooks and other general interest books usually provide overview information. They are good sources for gathering background information and gaining an overall understanding of a topic. Books and monographs usually have editorial review to insure quality. Some information goes out of date quickly. Textbooks and review are considered secondary publications.
Conference proceedings are the collected papers presented at a conference or workshop.
Their purpose is to get research results published quickly. Some conference papers are rewritten for later publication in a scientific or scholarly journal that is peer-reviewed. Some conference papers may be primary literature if they report the results of original research. Popular magazines do not require extensive prior knowledge or special expertise to understand. They often contain colorful pictures and graphics to appeal to a wide range of readers.