1) Download Steam and make an account.
2) Then launch Steam on your PC, and search "Doki" in the store, it will come right up. Download DDLC through Steam, add a desktop icon, Steam will set the game up for you.
3) if you can't find the game on your desktop, look in your Steam game library. If you don't see it there, search it again in the Steam store - this time instead of download it will say "Play". (If the desktop icon won't launch the game, launch it from the Steam store per #3)
4) Play DDLC, fall in love. Then cry, poop yourself, and slowly go insane.
Enjoy! :)