I open terminal and enter the following commands
sudo mongod
which then outputs
[initandlisten] waiting for connections on port
Before Mongo 3.6:
You may start mongodb with
mongod --httpinterface
And access it on
http://localhost:28017
Since version 2.6: MongoDB disables the HTTP interface by default.
Update
HTTP Interface and REST API
MongoDB 3.6 removes the deprecated HTTP interface and REST API to MongoDB.
See Mongo http interface and rest api