Serialize bits from input/output pin with VHDL
If you're struggling to catch the VHDL concepts, don't start with that kind of project!

Start smaller.  

First, flash an LED at 1Hz.  Now build a simulation for the same code.  Normally, you'd build the simulation first, but I know that most people really want to see some hardware working ASAP!

Now wire up a pushbutton switch to the FPGA and use it to stop and start the LED flashing.  Don't forget to debounce it.  Simulate first, then demonstrate in hardware.

Once you've done those two tasks you will have some more idea about VHDL, and can ask smaller questions about the task you want to complete, rather than just dumping a load of C code and asking for it to be converted into VHDL.