Hello,
In this path:
C:\Users\Alireza\AppData\Local\UnrealEngine\Common\DerivedDataCache
There are a series of folders I don’t know what they are but that has filled my C: drive entirely.
What are those and does it harm if I remove them?
The DDC stores version of assets in the formats used by the engine and it’s target platforms. It is kind of like the Shader Cache from UE3 but for each asset in your project. You can safely delete it but this will make your project’s take longer to launch on the first launch as UE4 will need to re-make the DDC. The following document will explain more about the DDC, what it is and how you should be using it.
For my personal home PC I use a Junction to point my DCC from my smaller SSD to my bigger data drive. Here is a link to an article that talks about Junctions, what they are and how to set them up.
Let us know if you have any other questions about this.