Typical parts for a Desktop computer (tower, not peripherals)

Typically to get started you are going to need several parts

• CPU also known as a processor, central processing unit (made of an algorythmic unit and a logical unit.
• motherboard (connects to all other chips) 
• Heatsink or liquid cooler for cpu if it is not packed in with the processor
• Case, tower. 
• Tower fans for the case and to go over the cpu heatsink if they were not bundled. make sure that the fan sizes match the case (larger fans are typically quieter when operating) 
• *Ram which must be compatible with the mobo (determined by clock rate)
• *PSU sufficient to power your mobo, cpu, and other devices (optical drives, hdd, sound cards, gpus) be especially careful considering out the capacity of the 12v rail (cpu and gpu use it heavily) 
• graphic cards
• Hard Disk Drive or Solid State drives 
• Optical drive if needed
• Sound card if desired(higher quality dedicated audio)
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Because cases are available in several standard form factor such as atx btx, pico and micro it is important to match the form factor of the case and the motherboard. Insure that the socket type on the cpu and the mobo match and the the maker of the mobo and cpu list them as compatible to avoid problems during assembly and operation of the computer.
When selecting ram make sure you match type (pin number and ddr series) and check that the motherboard is able to accept that speed of ram. If the ram is rated for a multiple of the motherboards base clock rate type then it will typically work fine, but it may not make financial sense to the quickest ram you can find if the motherboard does not support the rated clockrate( it will likely still work but it will run at the top rate supported by the motherboard unless you use overclocking with can lead to issues with overheating as well as short circuits. Once again make sure to get fans for your case to match the available mount points if they are not included with the case. you can often find fans with integrated leds One of the most important things to keep in mind the the wattage needed for the power supply, you can simply add together the power need by the motherboard, graphics, cpu, storage drives, and optical drives to come up with a range and add 20 to 30 percent to allow for longer life by reducing the time that the supply is running at maximum capacity. Leaving wiggle room will help in the long run if you plan on upgrading or adding to your computer overtime. Normally you will not need more than 750 watts for a machine using integrated graphics from the cpu or mobo, 900 for 1 graphics card, or 1200 for a system using dual or sli graphics cards.