How to open Android activity from Unity ?

Hello,

Let me clear that, i have followed so many tutorials & documentation, still i have not found my answer. So, i am posting here.

I want to make a simple android plugin that will load my activity of android project. I also want to call some methods also. But i don't know how to do this ? Can anyone help me ? Please post step by step if possible, because i have followed so many tutorials, still i am not able to get my result.

Thanks.