As part of the AFF system they have very extensive metadata describing the content of the data files that are accessilble via their system. To view the metadata for this filetype (Census 2000 Summary File 1) you can access their Data Sets page (displayed on the upper left side of the AFF main page.) Once on this page find the entry for this file type and click on the radio button to select it. A new menu sub-frame will appear with an array of things related to the data product, including an entry labeled "About this data set". Click on this item and a new window will open and it will be filled with an extremely thorough and complete description of this filetype (be patient, it takes a few seconds for all the data to load in the new window.) Included here is a complete listing of all the tables that comprise the data set. And, of course, there are also ways to then access the data from selected tables for selected geographies via AFF. You may well find the AFF access methods more suited to your needs to view and/or extract data. But even if you still want to access the data here via uexplore, being able to access this extensive metadata can be a great help in identifying the data that you are looking for and in obtaining detailed background information regarding definitions and methodology used to collect and tabulate the data.