Hi, OldCoalMiner, Welcome to Electro-tech-online.
While drawing the circuit diagrams (schematics), there are conventions. Whenever a wire symbol crosses another wire,, as per old practice, a bow (what you called
open circle)is made and then the line continues. where ever there is a connection at the crossing or T- joint , it is indicated by a darkened spot across it.
As per modern practice, a simple crossing of wires indicated is NO cross connection( I meant no
open circle). If dark spot is there, it is a cross connection. At places of T connection, even if the spot is not there , it is connection.
Hope this serves to have a start of how to study a circuit schematic.
an online free book indicated below may be of help to you
https://www.mikroe.com/en/books/keu/00.htm