Start here, and create your game in the emulator: 

https://felipemanga.github.io/ProjectABE/?url=new

Use the documentation to start writing code:

https://mlxxxp.github.io/documents/Arduino/libraries/Arduboy2/Doxygen/html/index.html

If you need help getting started check out this tutorial:

https://community.arduboy.com/t/make-your-own-arduboy-game-part-2-printing-text/7925

Use one of the image converters if you need bitmaps:

http://fuopy.github.io/arduboy-image-converter/

https://community.arduboy.com/t/ab-sprite-editor-public-beta/10374

http://www.andrewlowndes.co.uk/blog/graphics/arduboy-image-converter

https://www.crait.net/tochars/index.php

http://www.bloggingadeadhorse.com/TeamARGImgConverter/

http://www.bloggingadeadhorse.com/TeamARGTileSheetConverter/

http://www.bloggingadeadhorse.com/TeamARGSpriteConverter/

Post your game online, drag and drop a .hex file into a post:

https://community.arduboy.com/c/games/35

Share it on Itch.io with the embedded emulator:

https://community.arduboy.com/t/releasing-your-game-on-itch-io-play-in-browser-template/10488

https://itch.io/search?q=arduboy

Promote it on social media:

https://www.reddit.com/r/Arduboy/