Appium is an "HTTP Server" written using Node.js platform and drives iOS and Android sessions using Webdriver JSON wire protocol. So, before initializing the Appium Server, you must have preinstalled Node.js on your system.
When we download and install Appium on our system, it installs a server and it on the machine that exposes the REST API. When the clients send the command and connection requests, it executes that command on devices like iOS or Android and replies with the HTTP responses. To execute the requests, it uses a mobile test automation framework to run the app's user interface.
For Example, it uses Apple instruments for iOS, Selendroid for Android API 15 or lesser version, and Google UIAutomator for Android API 16 or higher versions.
Note: Appium uses the open-source library Selendroid to support older APIs because UIAutomator only supports API 16 or higher.
