How would I structure a Data Store?

Since datastores can save tables, this is very easy.

local ds = game:GetService("DataStoreService"):GetDataStore("DataStoreName")
local defaultItems = { -- this will be what the player gets if they're new to the game
"AwesomeHat", -- idk some random item name
"CoolBeans", -- another random one
-- add more of the items you want
}
local data = {} -- where all the players data is stored for everyone in the server

game.Players.PlayerAdded:connect(function(plr)
local tab = ds:GetAsync(plr.userId)
if not tab then tab = defaultItems end -- if they're a new player set to the default table
local found = false

for i = 1,#data do -- makes it so multiple data's aren't stored in the data tab
if data[i][1] == plr.Name then
found = true
break
end
end

if found == false then
table.insert(data,{plr.Name,tab})
end

end)

game.Players.PlayerRemoving:connect(function(plr)
local tab = nil
for i = 1,#data do
if data[i][1] == plr.Name then
tab = data[i][2]
brek
end
end

ds:SetAsync(plr.userId,tab) -- saves their data
end)

Hopefully that helps a bit..