What are the triangle indents on the wires connected to pins 1 and 4, also what the slider connected to first triangle indent means?

 

What you see is the circuit symbol for a TRS jack.

TRS = Tip, Ring, Sleeve

These are the electrical contacts to the plug that is inserted into the jack.
The triangle is NC (normally closed) switch contact. When the plug is inserted into the jack, the switch opens.

 

Welcome to AAC!

What are the triangle indents on the wires connected to pins 1 and 4, also what the slider connected to first triangle indent means?

They're contacts on the connector.

The "up arrow" on the top connection isn't a slider. It represents a normally closed connection that opens when something is plugged into the connector.