A graphics card is a device that produces video output to allow the user to receive feedback from the machine. In general, freelancers and small businesses do not generally need a powerful graphics card. Some professionals, like photographers and video editors, do benefit from a powerful graphics card for rendering, applying filters, and more.
An integrated GPU (iGPU for short) is the simplest and most inexpensive way to get video output. These are included in almost all consumer-grade processors. Every GPU needs memory, though, which can be on the CPU itself or, more often than not, can be your system’s RAM. Using the system’s RAM is much slower than using specialised memory. The RAM used by the iGPU is also unavailable to applications.
Integrated GPUs are however good enough for most people, and are what you probably want to use to work, watch a movie, or other light tasks.
Dedicated graphics card
A dedicated GPU, or discrete GPU, is an additional processor that helps with performing tasks associated with graphics. They’re generally much more efficient than an integrated GPU and also have their own memory. Laptops generally use a technology called scalable graphics that enables the discrete GPU only when graphics capabilities are more important than power consumption.
On the other hand, dedicated GPUs for desktops connect to the motherboard through PCIe, generally of the x16 variant. There are so many models of graphics cards out there that it would be impossible to cover them all. The two biggest GPU manufacturers, AMD and NVidia, only produce a handful of cards, known as reference models. They then sell GPUs and provide specifications to other manufacturers who tweak the original design to attain higher performance, add more memory, use a different type of cooling solution, and so on and so forth.
If you really need a graphics card (for example, you use your computer to also play videogames) then a mid-range model, like the GTX 1060 or RX 480, will do wonders for you, provided you have a 1080p display.