Am just a user of Moodle ... have not written any 'community authored' Moodle doc for anything ... so can't address/answer your questions about that, but, instead will ask you to do something before you become even more frustrated ....
Site administration link on front page.
Server
Environment
In upper right corner of Environment page, click update component.
Screen should refresh and send you back to the Environment page.
Set the drop down pick list (which shows your 2.8 listed first) and select
'3.7'
Upon selection Moodle will check environment again and refresh the page.
At the top of that page, what does your server check show for:
a. moodle (version)
b. database
c. php
Under the 'Status' column of that page, does any of the 3 show a Red check?
In report column of that page:
a. What does is say for database?
b. What does it say for php?
'Sos', Ken