Anti-seize is a paste you apply to the threaded mating surfaces of hardware to make sure it does not bind or seize. Anti-seize compound is commonly used on spark plug threads so that they are easily removable when the time comes for replacement. An exception to this rule is when the engine head is aluminum and the spark plug's body threads are stainless steel. Since anti-seize is a copper based paste, it places a third type of metal between two metal mating surfaces, and thus acts as a lubricant which causes plugs to loosen over time.
Remove the old spark plugs with your spark plug removal socket attached to a ratchet via a wobble extension. While spark plug removal varies from engine-to-engine, generally you will need to remove the coil pack that sits over the spark plug to gain access to the spark plug.
Insert the new spark plug into your spark plug socket, and then install into the engine head without applying anti-seize paste to the spark plug threads. The reason why you do not want to use anti-seize is because anti-seize contains copper, thus you are inserting a metal between soft (aluminum head) and hard (stainless steel spark plug) surfaces. This makes the anti-seize act as a lubricant between two metals with different thermal properties, causing the plugs to loosen over time. Loosened spark plugs rattle in the spark plug well, and can be damaged, even causing the electrode to break off.
Torque down the spark plugs to the rating as specified in your owners manual for your specific car. While modern platinum spark plugs are rated for up to 100,000 miles, it is a good idea to periodically remove and inspect your spark plugs for unusual wear or damage.
