What is this thing that goes near the ignition coil?

That is the spark plug. It is a device that fits into the cylinder head of an internal combustion engine and is responsible for igniting the air-fuel mixture within the cylinder. The spark plug consists of a central electrode, which is connected to the ignition coil, and a ground electrode, which is connected to the engine block. When the ignition coil generates a high-voltage electrical current, it flows through the spark plug, creating a spark that jumps between the central and ground electrodes. This spark ignites the air-fuel mixture, causing the engine to fire.