The Graphics card
The Graphics card or GPU is the component in a computer that handles all rendering and video output. In most use cases a GPU is a unnecessary as your CPU will have integrated graphics onboard that will suit a standard users needs just fine. however in certain applications where more horse power is required such as video animation, edition, and gaming a GPU will benefit your build immensely.
knowing what kind of GPU to buy is very important. If all you want is more monitor out puts and the ability to drive higher resolution displays then you would be wise to pick up a cheep 50$ card of amazon and know that that's all you have to worry about. for the higher end things you will have to look harder. For video editing and 1080p gaming a card like the R9 280x or GTX 970 are a solid choice. At the even higher end of things you will require one or even two GTX 980s.
knowing what kind of GPU to buy is very important. If all you want is more monitor out puts and the ability to drive higher resolution displays then you would be wise to pick up a cheep 50$ card of amazon and know that that's all you have to worry about. for the higher end things you will have to look harder. For video editing and 1080p gaming a card like the R9 280x or GTX 970 are a solid choice. At the even higher end of things you will require one or even two GTX 980s.
Moniter
People often over look how important a monitor is to the build of a computer. While a monitor does not directly affect the performance off a computer however it is your only way of interacting with the computer. A bad monitor will provide a simply worse experience all the time. Bad color acruacy, terrible off viewing angles and low resolution all are things that come with a bad monitor. for general use spend around 200$ on a monitor.