Open Collections and choose New collection. Choose a category and enter a name. Select Automatic to include matching items automatically, or Hand-picked to choose the items yourself. Save the collection.
In a hand-picked collection, use Add items, select the items and tap Add selected. Automatic collections follow their category and any rules you set. If an item is missing, check its category and the collection rules.
Use the collection menu to rename it or change its cover. Removing an item from a collection keeps it in your inventory. To record where something physically lives, use rooms and places.