Why does my directory command create a read-only file system?

Question

I am trying to install MongoDB on my Mac, however, despite following step-by-step instructions of the official documentation and of my course, my make directory command on the command line is not working to create the default /data/db directory. What is wrong? Here I will leave all the command line code, so far it has worked until the latest mkdir where instead of creating the desired directory a read-only file system is created.

aaronserpilin@Aarons-MacBook-Air ~ % sudo mv /Users/aaronserpilin/Documents/Web-Development/mongodb-macos-x86_64-5.0.2 /usr/local/mongodb
Password:
aaronserpilin@Aarons-MacBook-Air ~ % open/usr/loca/mongodb
zsh: no such file or directory: open/usr/loca/mongodb
aaronserpilin@Aarons-MacBook-Air ~ % open /usr/local/mongodb
aaronserpilin@Aarons-MacBook-Air ~ % cd ~
aaronserpilin@Aarons-MacBook-Air ~ % touch .bash_profile
aaronserpilin@Aarons-MacBook-Air ~ % ls -a
.           .viminfo        Library
..          .vscode         Movies
.CFUserTextEncoding .wallaby        Music
.DS_Store       .zsh_history        Pictures
.Trash          .zsh_sessions       Postman
.bash_profile       Applications        Public
.config         Desktop         node_modules
.node_repl_history  Documents       package-lock.json
.npm            Downloads       package.json
aaronserpilin@Aarons-MacBook-Air ~ % open .
aaronserpilin@Aarons-MacBook-Air ~ % vim .bash_profile
aaronserpilin@Aarons-MacBook-Air ~ % mkdir -p /data/db
mkdir: /data/db: Read-only file system
aaronserpilin@Aarons-MacBook-Air ~ % open /data/db
The file /data/db does not exist.