Hardware Descriptions
CPU
Connectivity
GPU
Display
PSU
The Central Processing Unit is the center of the PC. It carries out the instructions of any and every computer program by performing the basic arithmetic, logical, control and input/output (I/O) operations specified by the instructions. Many have different sockets and require different motherboards in order to function so its important to choose carefully. Some CPU's also now come with integrated graphics (GPU's) and will power most of the average persons graphics needs.
This is basically all preference. You can basically get any display to work with a computer through cables and adapters but what are you going to be using the display for. If its watching movies you're going to want to aim for a 4K monitor making surethe GPU ca power that. Or maybe competitive gaming, a 1080p 144hz refresh rate monitor which will show 144 frames per second on the screen making sure you dont miss any of the action. VGA, HDMI, DVI, and Display Ports are mainly what youre going to be using to connect your monitor so its important you get one of these beforehand as most monitors do not come with one included in the box.
This is really only important if you are going to be gaming or rendering complex geometry on your machine as most CPU's have some form of integrated graphics. Graphics cards use the PCI-E port on a motherboard and can take up a lot of space in the case if shopping in the higher tier market. Its important to plan ahead for this and choose a case which is going to support your graphics cards size and weight. Also different companies make their own versions of a card with their own tweaks and additions. Do some research before you buy and check the user reviews.
This is an important piece of the machine as you need to carefully purchase the right amount of wattage for your machine. If you undershoot you arent going to have enough wattage to power all of your parts. It doesnt really matter if you oveshoot the target its jut going to hit the bank a bit harder so its important to carefully measure how much youre going to need. Then theres the choice between modular ad non-modular, with a modular power supply you can attach ad detach cables at will, this is good for clean freaks who want their rigs looking clean and keeping cables to a minimum. With a non-modular power supply you are still getting all of the cables you are going to need but you dont have the option to attach more or take any off, this gets very messy and you will find yourself finding places to shove the left over cables.