Overclocking is the act of changing the clock speeds or frequencies of a certain component in a computer. It is usually done in the BIOS for CPUs/Memory, or using a specialized tool in Windows for video cards (such as MSI After Burner). Overclocking a component increases its speed, but if it is not done correctly, can make the computer run unstable, or can even damage components. Temperatures are the main thing to look out for while overclocking. If you do not have adequate cooling, the components will at some point overheat, which can cause failure. You also have to keep the voltages in check. Overclocking a component too far with stock voltage can cause instabilities. If the BIOS lets you, voltages can be changed for the CPU and other hardware. Increasing the voltages of a component will increase its heat output significantly.
Long story short, don't overclock if you are not comfortable doing so. Because doing something wrong can turn out to be very bad. Including giving a component far too much voltage, and literally frying said component.
Some manufactures have more lenient restrictions on their warranties when it comes to overclocking. Read your warranty well. For me overclocking is a hobby and very addictive i am so hooked i would not even use a computer that could not be overclocked seriously as you can tell i need help lol.You need to do lots of research and study it first i don't recommend anyone do it after say watching a youtube video or reading up on it for twenty minutes lol that's just asking for trouble.