How can i connect my Raspberry Pi to my Local Server on the Same Raspberry Pi?

Hello Guys,
I need help with my Raspberry Pi Blynk project.
I wanna install a Local server on an RPI, then i wanna control with the app GPIO/digital Pins on the Same RPI.
Do i need a script or scetch and how can i start and config that?
I have an RPI 3B+.

Thanks for help from a helpless newbie