Item Shop

The item shop is a in-game shop that allows you to spend Admiral Points to buy resources, development materials, repair buckets and other goodies. To access this menu, you can press L on most screens and select "Items". You can also get to this area by pressing L on the Admiral Room screen to access the Orange submenu, and choosing Items from the buttons shown - it's the third one from the top clockwise if you're playing the Japanese non-translated version. This will take you to the items screen, which is separated into two areas: the Inventory and the Shop itself.

Inventory

The inventory shows you all your awards, including medals, furniture coin boxes, combat rations, Mamiya and Irako Food Supply tokens, development materials and repair buckets just to name a few. This has a bookshelf-like appearance. You can "use" some items like furniture coin boxes (in which it'll award you with the amount of coins it contains) and turn medals you earned into screws for use in Akashi's Improvement Arsenal.

Akashi in her NPC form will appear as your item shop assistant. Tapping anywhere on the screen or pressing any button will make her get back to work. The shop button is located in the top right of the screen, under the status bar that shows your current resources button.

Shop

Tapping the shop button will transfer you to the items for sale list, where on the left is the name of the item with the description. On the right is how much that item costs. For example, 300 Fuel costs 100 Admiral Points while 1200 Fuel costs 300 Admiral Points. Same with real world spending, find out what is the cost effective way of buying resources for yourself as splurging on some resource packs is nice... but remember there's more than 20 items for sale - so plan ahead!

If you don't have enough admiral points, you will be unable to purchase the desired item. Akashi apparently does not give out freebies, it seems.