Two of the more complicated components in Symfony2 is the Form and Validator component. The Validator is created in such a way it "always" need an Domain Object with Constraints associated through metadata. This is explained in detail here. But there is another way. A way that resemble's the symfony1 forms. Where you could specify the validations directly in your form class.
Code is included in the post to show how to load in a few of the validators (like NotBlank, Email and Choice) and how to use them in the settings defined in the "getDefaultOptions" method.