How to tell my computer to run a program on fpga

It sounds like you dont really understand what an FPGA is. An FPGA is a field programmable gate array. Basically, it is block of programmable logic cells, meaning the user can program it to do pretty much whatever the user wants. Depending on the device, it will have 10s to about 2000 IO pins, allowing it to be connected to several interfaces at once. You would then create controller logic for each interface and logic internally to process that data before sending on through another interface. Some devices have high speed transceivers, allowing it to be connected to PCIe, ethernet (up to 100GB now on the newest top end devices) SRIO or any other high speed serial IO.

It is very common for the FPGA to be a slave to a CPU - with the CPU being the master controller for the system, and the FPGA being a large data processor. Because the FPGA has much higher data capabilities, it can handle far more data than the CPU.

It sounds like you need to read up on digital logic design, HDL coding and other things. Altera have many tutorials online, like here: https://www.altera.com/support/training/university/materials-tutorials.html