Hi there,
There are lots of free stamp bases that you can download and colour in an art program on your computer, you can for example
search dA for them. You can also use a
stamp maker like this one, it's great if you don't have an art program that you like using.
To make an image move you have to create separate images for all the different steps, then you put the steps together as an animation. Some art programs, like Photoshop can make animations. If you don't have a program like that you can use an online image modifying program like
http://www.iaza.com to put your images together.
I think that the easiest way to make growing adoptables is to use
http://www.photobucket.com, I explain how to do it
here. Some other people explain some other ways to make them grow in the same thread as well.