it can be explain by example folows:
func. spec. like what a particular link is supposed to 
do...as on login window, link of "LOGIN" is to lead to 
logged in page, so it is functional specificaton of this 
link.
in case on non func. spec. what would be name of that link 
leading to logged page...it will be "LOGIN" or "OK" or some 
other what is required by customer. means LOKK and FEEL not 
working.

Requirement that specifies a function that a 
system/software/component must be capable of performing 
whereas a software requirement that describes not what the 
software will do,but how the software will do it, for 
example, software performance requirements,software design 
constraints, and software quality attributes.

checking the each  specific  functionality of the appl as 
per the requirement is functional spec

checking the UI and usability,reliability...etc are non 
functional testing

impressive@