Hey Drejina, Appium is an open source tool for automating Android/IOS platforms. It can be used to automate mobile browser, native and hybrid applications for both Android and IOS. It can be used really well with Selenium Webdriver as it uses the Web Driver API and anyone with knowledge of Selenium WebDriver can easily work on Appium. So there is no need to learn a new API to automate your mobile Applications.
Appium is a cross platform tool, thus enables user to write tests for multiple platforms (Android/IOS) using the same WebDriver API. So you can use the same Webdriver based framework for mobile automation with Appium, if you already have an existing WebDriver framework for your Web Application.