Read the summary: A full description or abstract of the study's subject matter or intellectual content. The main goal of the summary is to give the user a clear sense of what the study is about, including the purpose of the study, the major topics covered, and what questions the principal investigators attempted to answer when they conducted the study. Note that summaries typically avoid attempting to address issues of how data might be used, who might be interested in the data, or any evaluative comments about the worth or usefulness of the study.
How to Use a Codebook (from Princeton University Library) explains what information you should look for when using a codebook. The codebook provides useful information about how data were collected and organized. The questionnaire reveals what the investigators were asking and trying to analyze.
Note:You can download the publicly available datasets, e.g., the federal census. If the dataset is restricted, only current UNO faculty and students may download the data.