You can connect with just mongo if you try to connect to a running mongod. It looks like, in your case, no mongod is running on your local host at default port 27017. That is why you have to start it.
You can connect with just mongo if you try to connect to a running mongod. It looks like, in your case, no mongod is running on your local host at default port 27017. That is why you have to start it.