Once you installed Jenkins Server with Ubuntu, perform the steps as mentioned below to configure your Jenkins Server.

Step 1: Collect Public IP Address of the droplet from DigitalOcean Cloud screen. In my case IP Address is 157.245.129.193

Step 2: By default Jenkins runs on port 8080. To start Jenkins on port 8080 provide below given URL in browser.

http://publicip:8080

In my case it is: http://157.245.129.193:8080

As mentioned in above screenshot you can get the password of user from file: /var/lib/jenkins/secrets/initialAdminPassword

To do that first login to your server and run below command.

Copy password, paste it in browser and click on Continue.

Step 3: Choose the option, Install suggested plugins

Step 4: It has started installation of all the important plugins. Wait till finished.

Step 5: Now Create User and Click on Save and Continue

Step 6: It shows you Jenkins URL

Click on Save and Finish

Step 7: Start using Jenkins

Your Jenkins is ready now, you can use it to configure New Item.