Hello,
1/ You can click them to use them and see what happens

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2/ grey item -> sell it to a vendor NPC
3/ Those items upgrade your alchemy tool. I recommend
this one, if you have to choose one from the alchemy quest. It's not necessary to buy all 4 upgraders as a low level alchemist. But you'll need them all when you'll reach lvl 40 in alchemy (if i remember well, when you'll buy the last alchemy tool).
4/ Loot pets are sold in the item shop. There's a bird, a little goblin and a fairy. You can also buy a very usefull manual, so that the loot pet will be able to gather herbs aswell.
Welcome to Allods, have fun

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