How to Navigate Form Xamarin.Forms Page to an Android Activity on button click event?

I was created a new project using Xamarin.Forms(Portable). When I run (projectName.Android) it initially displays the page from (projectName(portable)) i.e., Runs the GetMainPage() method from App Class. The GetMainPage() method contains a button on content layout. And i also have a new android activity in (projectName.Android). Now, I want to navigate to my android activity when i click the button in projectName(portable)i.e., Button from GetMainPage() method. Please help me!