https://www2.census.gov/programs-surveys/acs/summary_file/2018/data/5_year_seq_by_state/Michigan/Tracts_Block_Groups_Only/
Where can I find the documentation that shows what each of these tables refer to and what the variables are?
To add to where Mark pointed you to - I had a need for this as well and to make it easier for myself I created an "Appendix C" of the Appendices that uses the supplied documentation to create the table structures. You can get it online here:http://gisdiva.com/downloads/acs2018-5yr/
(or direct link the Excel file http://gisdiva.com/downloads/acs2018-5yr/!ACS_2018_SF_5YR_Appendices.xlsx )