How to create 2D animation pictures from PNG?

Hello,
I am new to 2D animations. I have a few images in .png format. I am planning on creating 2D animations for a game.
How can I create 2D animation pictures from Png? What software should I use and where can I download it? Also, could you please help me with some instructions on how to create 2D animation pictures from PNG.
Thanks.
