To start the Jenkins server please follow the below steps:
First, you need to start the Jenkins service from the terminal. Open the terminal in the VM and then run the below command:
sudo service jenkins start
Now open the browser in the VM(you can open Mozilla Firefox) and in the address path give the below path:
It will open the Jenkins login page and the username and password will be already filled(no need to make any change). You can click on login and start working with Jenkins.
I hope this resolves your issue.