Synthesizing the design

To synthesize the design, go to the "Processing" menu and select "Start Compilation", or click on the purple arrow icon in the toolbar. Synthesis should be quite fast since the design is small. After compilation is successful, you should have a new .sof file in your Quartus project directory. It should be 703,642 bytes long.

Uploading the bitfile

Plug in your DE0-Nano board via the USB connector. Now, go to the "Tools" menu and select "Programmer".

In the top left of the window that appears, you should see "USB-Blaster [USB-0]". If instead you see "No Hardware", click on "Hardware Setup..." and (re-)select your device.

Now, select the .sof file in the list, ensure "Program/Verify" is checked, and click "Start"! This should take about a second.

The FPGA is now programmed with your design! (This only programmed the SRAM though, not the onboard EEPROM — so the design is only stored until power is turned off.)

Note: In the future, you can use the command script de0-nano/program.cmd to quickly program the FPGA's SRAM with your .sof file (it uses the Quartus command line programming utility).