What is this symbol: semicircles facing each other?
These are "solder links" and could look like:



Note how the top right one looks the most similar to the symbol from the schematic.

These are copper shapes on a PCB.

If you don't do anything these structures will be an "open" so they make no connection.

But using a soldering iron and some solder it is easy to apply some solder and make that connection.

This can be used to connect / disconnect certain parts of a circuit on a PCB and so set certain options, for example to feed a certain voltage to a line (or not).