Modifiers are simple structs F_Modifier which are stored in items and can be retrieved through interface I_ItemHasModifiers.

As an example let’s take a look at SteelBoots item blueprint, it has array of modifiers.

It means that whenever character equips SteelBoots, 1 point of armor and 10 points of health will be added to stat modifiers values.

But how this array get here? Let’s take a look at parent of SteelBoots which is Item_Armor.
It implements interface I_ItemHasModifiers, which requires to implement function GetModifiers.

Array of modifiers in image above is returned through this interface function.