There are 45000 indicators that can be selected. A top-level search form
In the edit form for a Census entry you can select which indicators to use. The indicators are categorized and you can restrict your search for a particular category of indicators, e.g. to search for indicators in the group "Median Income by Place of Birth in the United States" enter:
category:b05006 your search term
You can specify that the value shown for a particular indicator is a percentage of another indicator. Say for example you have population data by gender (B01001_002E, B01001_026E). You can specify that the indicators are a percentage of another column by appending ":%<column>" to the indicator id. For the below indicators we append ":%1" (zero based numbering) to use the second column (population).
B01001_002E:%1 //male population
B01001_026E:%1 //female population
The Headers field allows you to specify an alternative set of indicator names, one per line, to use in place of the names from the Census Bureau.
The data is selected based on a geography specification - e.g., state, county, tract, etc. More information here -