In fact, you can set what you want where you want as long as you set the good structure in your mod's files. (for example, if you set the sprites in items, you need to put it as items/sprite.png for example, and not sprites/sprite.png)

So, basically:
- mod folder is for the .xml things
- sprites for the mobs / characters sprites
- items is for the item's pictures
- soundfx is for the music & other sounds.

So, the only folder you NEED to have is the mod one. Other aren't necessary.

引用自 Vehemens：

In fact, you can set what you want where you want as long as you set the good structure in your mod's files. (for example, if you set the sprites in items, you need to put it as items/sprite.png for example, and not sprites/sprite.png)

So, basically:
- mod folder is for the .xml things
- sprites for the mobs / characters sprites
- items is for the item's pictures
- soundfx is for the music & other sounds.

So, the only folder you NEED to have is the mod one. Other aren't necessary.

Thanks for the help, but I've got it sorted out now. I was a little confused as I assumed that the pictures for the items were to be placed inside the "sprites" file.