The images below represent some of the main components of a desktop PC, however the same parts exist in a laptop just significantly smaller. it is important to understand the relationship between the internal components.
This image shows a desktop PC with the inspection cover removed. You can see a number fo the parts that make up the PC.
This image shows an example of a motherboard taken from a desktop PC case. You can see the various sockets used for connecting power and other components. A more detailed look at this in the Motherboard Section.
The processor shown here is an Intel Core i7, it has a clock speed of 2.93Ghz. The silver surface mates to the heatsink once the processor is installed in the ZIF (Zero Insertion Force) Socket on the motherboard. Prior to placing the processor in place a film of thermal paste must be applied to the silver surface, this acts as an insulator between metal surfaces and helps dissipate heat. When installing a processor you must be careful not to bend the pins. More about the role of the processor in the CPU section.
A number of desktop and laptop manufacturers had discarded this device as they take up a significant amount of space and modern software is either as a service or downloded from the internet. The only other reason to have a 'Burner' in your machine might be to create a backup, however with harddrive being cheaper this is often a better option. When was the last time you burnt a disc?
The graphics card market is almost as the games industry. Graphics cards come in a wide range of specifications. Most modern cards can delivering brilliant graphics at a relatively low cost. Utilizing a graphics card rather than the onboard graphics which some motherboards have reduces the memory usage in the system, which improves performance of the computer.
Some audio enthusiasts make use of separate sound cards to improve sound quality and also reduce performance drains on the main system.
To be able to interact with the computer we need some form of input, however these are not internal devices in a desktop PC. Standard methods involve a keyboard and mouse.