A functional specification defines how the system will be used, and so is focused on user needs related to business requirements.
A technical specification defines how the system will meet the functional specification in terms of hardware, software, protocols, and performance metrics.
For example, a functional requirement might be for creating documentation that is suitable for both commercially printed marketing sheets and online viewing by clients, that imports raw data from the production unit monthly reports, and cannot be modified except by (specific job function) once published.
The technical specification might state that this document is created in Word using macros to import data from an Oracle data base based on date, using a defined read only document template maintained by Marketing department and stored in a share folder. Outputs are in Adobe pdf format with security settings of x and in nnn format as specified by the current printer.