During your time with Mortal Shell, you will be finding and collecting items throughout the game’s dark world. Fallgrim and beyond is packed with goodies that are both left behind by enemy corpses, and found hidden in chests and hidden away in statues and chambers.
The description for every item in the game offers some information on its lore, but the effect of its usage is not revealed until you use them for the first time. For example, Weltcap is one of the first plants that you will encounter, and one of the few resources that will regenerate once you have picked it. However, it will require you to use it before it reveals what it does.
There is also a familiarity system in place for items. Using one for the first time will unlock the tooltip for it, and it will also add to your familiarity of the item. If you continue to use consumables, it will continue to gain familiarity, and the game will confirm how many more times that you need to use it to gain full familiarity.
Once you have gained full familiarity, you will unlock the full form of the item. This means that it will become more effective as a result. For example, if you use an effigy to summon a different shell, using it with full familiarity to it will also grant a bonus that causes you to take less damage than usual from enemies.
In some cases, items will change completely. For example, the Tarspore is another plant that routinely grows around Fallgrim. On the initial use, it will hurt you for 40 poison damage over 16 seconds. After becoming familiar with it after two uses, it will then grant you immunity from poison damage for two minutes on use.
The mechanic is attached to all items in the game except the weapons, and the only way to improve your understanding on any of them is by usage.