I have already installed Mongodb on my mac but the process is currently not running. How do I start the Mongodb service so that I can start using the commands?
Try the following steps in Terminal:
which mongod
This will output the path to your mongod, but if it is not in your $PATH the command output will be empty. So you need to find your executable:
find / -name 'mongod'
In the output of this command, you will see many lines, one of which will be like bin/mongod, e.g. /usr/local/mongodb/bin/mongod. In that case take the whole absolute path and do the following:
echo "PATH=/usr/local/mongodb/bin/:$PATH" >> ~/.bash_profile
. ~/.bash_profile
Then try again:
mongod --dbpath /your/path