The second way to get Diablo 4 Aspects is to Diablo 4 items use an Occultist to extract them from items you find on your travels, which already have an Aspect attached. You can see this in the item description, along with details of what benefit the Aspect provides when imprinted to an item. Note that extracting an Aspect from an item by following the process with an Occultist will destroy the original equipment, placing the Aspect in your inventory for future use. Aspects obtained in this way are generally more powerful than those unlocked in the Codex of Power, but they can only be imprinted into one item.
To imprint Aspects in Diablo 4 with an Occultist, you need to have at least one available in your Codex of Power or inventory, along with a rare or legendary item of the correct type to receive it. Each piece of equipment can only be imprinted with one Aspect, so you can't stack up the effects using a single item, though of course you can have multiple items equipped with different Aspects spread across them.
Imprinting an Aspect will cost you gold, along with the rare Veiled Crystal crafting material, which is generally obtained by collecting Diablo 4 salvage from rare weapons and armor. Note that while it costs 10 Veiled Crystals to imprint an Aspect from the Codex of Power, you only need two to buy Diablo 4 items imprint an Aspect from your inventory, so this process is slightly easier and less costly in terms of materials if you're using an Aspect you previously extracted.