i have to create complex form having 20 fields and css designs between fields, and each fields have separate <div> . is it possible in easy form generation method in fuel using fieldset?
No, not in Fuel v1, the form template is rather limited. The v2 fieldset supports custom renderers, and support any format you want. You can use that in a v1 app at the moment, but there is no documentation as of yet.
Using v1, the only option is to pass the fieldset to the view, and either write our your HTML and generate individual fields: