Stickery is a very easy to use app for creating your own stickers.

As you can see in the first screenshot, you will be presented with a blank canvas. Just take a photo or select an image from your gallery and you can start editing immediately.

There is also an option to use the built-in editing tools such as:

Select a shape like a circle, rectangle, star, heart, etc. 

Add texts and customize its color, size, and border.

You can also customize the background and border colors.

When you're done editing, you can save the result in a new sticker pack.