You can upload a png with 6-view spritesheet (see example) using any of the 3 UpLoad buttons on the grid. The program detects each side automatically but the sprites need to be set up like this:
To get a Sprite file like this perfect, I suggest to build the model within 2-3 images (easiest) and export the Ortho Png to get this file if u want to modify it on Photoshop or Aseprite.