Content is the indication of the collection the item belongs to.
When adding a new stock, there is a field called 'Content' that represents the connection between the inventory sample item and the stocks. This category is mandatory, you need to make sure that it is linked to the right item in the inventory.

When adding stocks using the import function, the content of the stock has to be stated in the import template file under 'Inventory collection' and "Inventory item name or SysID" 

Content type defines the types of stocks that can be stored in a certain box connecting a box to a certain inventory collection.

Filling the 'Content type' field simplifies your selection when choosing a box for a newly added stock.
In the 'Suggested storage locations' drop-down menu, the boxes with the content type that fits the content of the stock will appear on the top and you won't have to choose from a drop down of potentially hundreds of entries. Choosing a content type to a box does not limit your ability to place any kind of stocks in it, it just helps making the process of adding new stocks simpler.

In a stock's page you can click on 'Edit' and choose to enter the name of the item you want to connect to under 'Content' (it will start giving you possible options after you type in 3 first letters). 

If you want to do it for multiple stocks at once - update them by using the Stocks update function, filling the "Inventory collection" and "Inventory item name" (or the "Inventory item SysID") columns.
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