Take a moment to review the components in the circuit diagram. This illustration is meant for referencing wired connections - The length of wire, position and size of components are not exact.
The PAM8302 amplifier connects to the + and - sides of the mini speaker. Route power by connecting VIN to 5V on the PowerBoost 1000C and then Gnd to G.
PowerBoost 1000C hooks up to pins #2(5V) and #6(ground) on the Pi.
The slide switch will need to connect to Ground and Enable.
Battery connects to the JST port next to the USB port on the Powerboost 1000C.