Sorry for the confusion with this. We understand that the current inventory system in the game lacks a comprehensive explanation. In the future, we plan to introduce a tutorial or prologue to thoroughly teach players all the mechanics. For now, here's a clearer explanation:
To access your inventory, press the TAB key. You'll find quick slots at the bottom of the inventory in a 1x3 grid. Place items in these slots to access them. Press Q to open the quick slots, where your items will now appear at the bottom of the screen. Select your desired item using the mouse.