For creating a basic blender. Graphic card is mandatory?
No! It can speed up the render process, especially using Cycles render engine.
But with the new EEVEE render engine, you can also create amazing illustrations.
With a good CPU you can do a lot. And if you have a GPU also, then Blender can automatically divide render task to both of them.
And for studying Blender you can use a simple machine. But it can be slow sometimes and consumes a lot of memory.
Thanks!
Note that it is not really necessary as @FedPete already said. But if you have an integrated graphic card it may still use it. I see Windows processes using GPU when I configure Blender to use mine, and it somehow speeds the process.
But note that most probably I would work better if I had twice or trice the memory (currently using 8 GB) and a bit more of free space on disk, since files and textures start consuming that space really fast.