If you're just starting out, then you've gotta begin with the basics: blinking a few LEDs, etc. From there you can progress to more and more complex circuits as you learn to code in VHDL or Verilog.

I'd recommend buying a couple of 2nd hand books on VHDL and/or Verilog to get familiar with the syntax. There are some good free books too:

http://freerangefactory.org/pdf/df344hdh4h8kjfh3500ft2/free_...

This little book is great if you're interested in how to build video game hardware for FPGA:

https://gumroad.com/8bitworkshop#JGZkq

I also have a repo of examples I wrote for the DE10 Nano:

https://github.com/nullobject/de10-nano-examples