This video explains and show you how to use air dry clay with mould shapes and how to paint with chalk paint. For any round surface when you sticking the moulds would be good to use UHU all purpose glue and hold for 5min when glue got sturdy. After painting the pot and mould with paint wait till paint will dry and with masking tape stick the mould to hold till it drys through the night because air dry clay when it dries it shrinks and might get out of the surface or crack. but that is not a big problem you can leave it as it if your aiming for old rustic look or you can fill it with hot glue. After all dry use protector like varnish or wax to go around the pot. I would recommend for outdoor use the varnish and for indoor wax.
For this project I use mermaid and classic elements moulds if you like the look you can purchase mermaid moulds at our store http://www.beecreativearthub.com/product/sea-sisters/
air dry clay http://www.beecreativearthub.com/product/air-dry-clay/
chalk paint http://www.beecreativearthub.com/product-category/fairy-chic-chalk-paint/