Install and Configure Jenkins using Jenkins.war if you have not installed Jenkins yet.
Once installation is successfully completed with initial configuration, On Jenkins Dashboard, click on Manage Jenkins
Click on the Global Tool Configuration Link.
There are four section available:
Update: It provides list of Plugins that have updates available to install
Available: It provides list of available plugins that are not installed yet. To install a Plgin, just select a checkbox and click on Install without Restart or Install after Restart.
Installed: It provides list of plugins that are already installed
Advanced: This tab provides HTTP Proxy Configuration and feature to upload the plugin in case plugin is already downloaded.