Also in answer to one of your questions, Thermal Compound and Heatsinks are both used to keep certain components cool. Usually the CPU and GPU. There are many types of heatsinks, but the ones I've seen have copper pipes to absorb heat, and then it's spread across a bunch of metal plates. The thermal compound is the catalyst for heat transfer. Without it, the amount of heat moved from the CPU or GPU to the heatsink would be much lower. So it's always a good idea to check your thermal paste every once in a while, just to make sure it isn't cracked and dry. If this occurs, it loses some of it's heat moving abilities which can cause components to overheat. This is very common in laptops if they are not serviced in 2 years or more.
An image of a heatsink: (A large one, but still a heatsink haha)
heatsink - Google Search