E.g. DP02, DP03, DP04, or DP05. A full list of tables can be found here
E.g. B01001A_013E, DP02_0011PE. A full list of variables can be found here
E.g. state, county, or county:*&in=state:26, or US to group; single geography such as state:26 or county:163&in=state:26; or specific GEO_ID. A full list of areas can be found here
Your API key here
This connects to the US Census Bureau API, please review the Census documentation