Jenkins is such handy tool which can be easily extended via adding additional plugins in order to accommodate more functionalities. E.g. including Git as SCM option, JUnit plugin etc. This can be easily done by selecting the option Manage Jenkins - Manage Plugins as shown below.
Click on the Mange Plugins from Manage Jenkins screen. This will take to the page where all the available plugins are listed out. Click on the available tab and from the available list of plugins choose the plugins which are required to be installed. E.g. select the Github plugin as shown below and click on install without restart button at the bottom of the page. This will download the github plugin and installs in the Jenkins.
As you click on Install, the download will begin.
Once the installation completes, you will see a Success message.
Now, open up any build job created and click on Configure. The Git option will be added under source code management.