I never understood about this command

How to use it
/fill [location] [location] [block name]
Then it will fill the locations with the block you selected. I have used this command lots of time

I still don't understand it. Even if you told me how to use it.

Then it will fill the locations with the block you selected.

Here is an example:
/fill ~~30 ~~30 ~~30 tnt
This will fill a 30x30x30 area near you with tnt

Change the numbers for different dimensions, like 3x4x2 would be ~~3 ~~4 ~~2
Change the last word for a different material, so you could do dirt, or red concrete or any other block
(At least in bedrock, I think it is the same for Java)

Umm............what? you see I'm not really a command nerd.