How to create Shop Categories

All you need to do is copy the default category

gems-menu:
  enabled: true
  default: true
  title: "&e&lGems Shop"
  size: 27
  fill:
    enabled: true
    material: BLACK_STAINED_GLASS_PANE
    durability: 0
    name: "&7"
  items:
    infoandbalanceItem:
      material: SUNFLOWER
      durability: 0
      skulls: false
      headDatabase: false
      skullOwner: ""
      customData: false
      customModelData: YOURIDHERE
      name: "&eWhat is the Gem Shop?"
      lore:
        - "&7The Gem Shop sells you items"
        - "&7you can not get in /shop."
        - ""
        - "&eYour Gem Balance: &b&l%star% &f%gems_formatted%"
      # Set to false so the menu knows this is not a buyable item
      buyable: false
      slot: 4
    '1':
      material: STICK
      skulls: false
      headDatabase: false
      skullOwner: ""
      customData: false
      customModelData: YOURIDHERE
      data: 0
      glow: false
      itemsAdder: false
      name: "&dMagic Stick"
      lore:
        - "&7Be special and buy a stick for %cost% gem"
      message:
        enabled: true
        broadcast: true
        text:
          - "&e%player% bought %item% &efrom &f/gemshop&e."
      action:
        # If enabled will use this instead of commands
        enabled: false
        actions:
          - "[console] give %player% stick 1" # gives the player an item from console
          - "[message] %prefix% &e%player% bought %item% &efrom &f/gemshop&e." # sends a message to the player
          - "[close]" # Closes the inventory
      commands:
        - "give %player% stick 1"
      cost: 1
      slot: 10

Then change default to false to make it not open with /gems shop

default: false

Then add an item in the default category to open your new category

'2':
  material: ARROW
  skulls: false
  headDatabase: false
  skullOwner: ""
  customData: false
  customModelData: YOURIDHERE
  durability: 0
  glow: false
  itemsAdder: false
  name: "&dOpen your menu name"
  lore:
    - "&7Open your menu name"
  action:
    enabled: true
    actions:
      - "{openmenu:menu-name}"
  # This is needed to make it not a buyable item
  # by default this is set to true for all items for compatibility
  # with older versions of the plugin when updating
  buyable: false
  slot: 15