You mean "use" an fmt tag, right? So what's the problem? You posted code but didn't tell us what the problem is.
Also, why are you using jspx format? That format is not intended for hand-coding but for use as an intermediate format or for machine-generated code. You should be writing jsp pages not jspx documents.
I have created fmt.tld in WEB-INF and also declared taglib in add.jspx but gives error "the markup follwing the root element must be well formed.". can you tell me how to insert taglib here.