Open the Terminal and type brew update.
downloading Mongo brew install mongodb
create the "db" directory. This is where the Mongo data files will live. Ensure that the directory is set up in the right place so that Mongo can find it

sudo mkdir -p /data/db/

Make sure that the /data/db directory has the right permissions by running

$ sudo chown -R `id -un` /data/db

Run the Mongo daemon, in one of your terminal windows run mongod. This should start the Mongo server.
Run the Mongo shell, with the Mongo daemon running in one terminal, type mongo in another terminal window. This will run the Mongo shell which is an application to access data in MongoDB.
To exit the Mongo shell run quit()
To stop the Mongo daemon hit ctrl-c

Note

you can override the default db path using the --dbpath argument of mongod( or use a config file).

mongod --dbpath /var/lib/mongodb/data/db

start using mongodb see my github:
https://github.com/HoweZZH/CS546/tree/master/lab3

recommendation:
Robomongo a MongoDB GUI management tool