How do I create partition using gparted or fdisk?

I was trying to create a partition using gparted but it wasn't allowing me. I logged in through root user and when I tried to create a partition, it won't let me.

And when I tried fdisk, I was able to create a partition but that crashed my storage. Hence I wanted to ask if there's some wy I can still reload the machine. I think my OS files are still safe because I created a partition for the OS in the beginning. It's the main stuff that's lost. What should I do? Also, what things should I take care of while creating partitions so that I don't crash my storage in the future?

Please let me know.