As mentioned, this is a very technical module! You will need to have a working knowledge of web technologies such as HTML, CSS, JS, PHP, and the Smarty templating language. How much and exactly what you need to know depends on what you're trying to do. The module tries to make it as simple as possible to create and manage your field types, but you will need to have technical experience for the more advanced stuff.
Secondly, you must be using Form Tools 2.1.4 or later of the Core.