One of my old project MonkeyWarp (playable on itch) is open sourced on GitHub. It might mot be the easiest project to dive-in, but if you have some questions I'll try to answer them.
I plan to create some tutorials and more simple demo projects
To draw things on screen, you need to add some code to the "src/main.js" file. For example:
var map = getMap('map'); // get the TileMap named "map"
draw(map, 0, 0); // draw map at position (0, 0)
sprite(153, 64, 32); // draw sprite 153 (from tilesheet) at position (64, 32)
Full documentation can be found here
You can add png images in the "assets" folder of your project. Pixelbox will load these automatically, and you can draw them on the screen with some code like:
draw(assets.mySprite, 0, 0);