This is a step by step guide for manually adding a buff to a primal item such as armor. Geared mostly for people with little to no experience with the graph. Can also be used for consumable items, see below.
Add a buff to an item on equip
Check "Use Blueprint Equipped Notifications"
Click V+ to add a new variable
Set the type of variable to "PrimalItem"
Name the variable whatever you want
Ctrl+Drag Variable for "Getter's". Alt+Drag Variable for "Setter's"
Need 1 Getter & 2 Setters
Right click empty graph area and select "Event BluePrint Equipped"
Right click empty graph area and select "Event BluePrint UnEquipped"
Drag from input of top setter and select "Get Reference to Self"
Connect Getter to bottom setter input. Drag from same getter and select "Get Owner Inventory"
Right click graph area and uncheck "Context Sensitive"
Drag from Owner inventory and select the "Get Owner" under "Components", NOT "Actor"
Drag from Get owner, re-check "Context Sensitive" and select "Cast to PrimalCharacter"
Do it twice so you have two "Cast to PrimalCharacter's"
Drag from top "Cast to PrimalCharacter", un-check "Context Sensitive" and select "Static Add Buff"
Drag from bottom "Cast to PrimalCharacter" and select "Deactivate Buffs"
Connect wires as shown and reference your buff
Variable connections highlighted to help see connections
If you want to add more than 1 buff. You can use just one Deactivate buff by setting the type to "PrimalBuff". be careful though as this will deactivate any and all buffs the character currently has active including those that are not part of your mod.
This will add the buff when the item is equipped, deactivate it when unequipped.
Change "Event Blueprint Equipped" to "Event BluePrint Used" and delete the unequipped sections above to use on a consumable item.