Until now I am following the nerdy nights tutorial and the adaptation for CA65. In those tutorials the authors give you a chr file for the graphics. To put it simple, in the CHR file you will put all the graphics that you will use in tiles.

Here is an example:

The application that is showing the chr file is yychr, and you can get it from it's official website (it is in japanese, but chrome kind of translates it in real time). If not here is an alternative.

I tried to create a new CHR file from scratch BUT as it is not completly filled it creates kind of a problem with memory, so I took the Mario chr file and started to edit it. I created a simple character in 5 minutes (my daughters want to be the ones that creates the definitive character for the game, so this is something I will use for testing and developing).

Editing this will also take a HUGHE ammount of time, but in this hobby you enjoy the trip.