I made an inventory item by myself, made the image(sprite) for it as no.3, and whenever I click on it in test mode, there nothing happens ???
Please BE MORE SPECIFIC.
What exactly have you done so far? Have you:
Assigned the sprite to a new Inventory item (or changed the sprite of an existing one).
Given the Item an Interaction.
Added that item to the player's Inventory.
I'm also a little fuzzy about what you mean by "whenever I click on it in test mode, there nothing happens". Do you mean you can't set the item as active, that the item's interactions don't run (by default, you should only be able to run the 'Look at Item' interation - is there one?), or that the item doesn't trigger inventory interactions in Characters/Hotspots/Objects?
I assume that you are trying to pick the object in a room, aren't you?????
or are you trying to use the object somewhere???
for the first question you should create a object and then assign some action.
for the second you must manage the hotspots with the inventory object.
In both cases the help is in the manual,
good luck. ;)