I have watched several videos on Youtube about this issue and none of them have worked. I know that I could not create mkdir -p /data/db because it will show me read-only due to Apple's system updates. You will find below what the terminal shows to me when I try to run a local server by using mongod. In the other hand, I can use mongo command and it works fine.
click here to see an image for the codes that appears when I use the mongod command