Once you have identified your topic and corresponding variables, you need to determine if you can find data on the variables of interest. You can search databases (see some at the end) and or can collect your own data. For example, publicly traded companies must report their financial data (e.g. number of stores, sales, etc.) to the SEC. Sports statistics are plentiful. Movies and other forms of entertainment (Fortnite) often report revenue numbers and usership engagement. Mission agencies, denominations (e.g. Southern Baptist) often have congregational membership figures available.
Free, public datasets can be found in many places. Please refer to the Data Sources tab (see left-hand column) to get started. Remember, the reference librarians can be a huge help! Use the "Schedule Appointment" box to the left to find tome to meet with your librarian to help you find a working dataset for your use.