Hello to store an item  go to your Edit button 

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That is the little arrow under the Champion area 

When you want to store an item you click on it the go to the item you want to store 

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When you store it  it will go to the Protected Lands  

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That is located on the top left of your game screen during Edit Mode 

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(Edited to include last Picture )

After you have placed the items you want stored you can exit edit by hitting the arrow again.

When you want to retrive your items you can again hit  edit button and reverse the process.

Also the Little i in the top left of protected lands has information 

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