Help with getting players in server?

Your script should be put into serverscriptservice, not serverstorage. You shouldn't be using :WaitForChild() if you are checking to see if an item exists. :WaitForChild() will wait forever until that item exists, even if it will never exist. If you are checking to see if an item exists, then use :FindFirstChild(), if you know an item will eventually exist and hasn't been created/loaded yet, then use :WaitForChild(), otherwise your script will wait forever.

This should fix your problems.

local sword2level = 5
local sword3level = 10
local sword4level = 20
local players = game:GetService'Players' -- If the player service doesn't already exist
print("0")

while wait() do
    repeat wait() until players.NumPlayers >= 1 -- Wait until there is 1 or more players in the game
    for _, player in pairs(players:GetPlayers()) do
        print("1")
        local shop = player:FindFirstChild("Shop")
        if shop then
            print("2")
             local stats = player:FindFirstChild("leaderstats")
            if stats then
                print("3")
                local level = stats:FindFirstChild("Level")
                if level then
                    print("4")
                    level.Changed:connect(function(playerLevel)
                                    print("5")
                                    if playerLevel >= sword2level then
                                        print("6")
                                        shop:WaitForChild("KnightsSword").Value = true
                                    elseif playerLevel >= sword3level then
                                        shop:WaitForChild("ShadowDancer").Value = true
                                    elseif playerLevel >= sword4level then
                                        shop:WaitForChild("OrcBlade").Value = true
                                    end
                                end)
                end
            end
        end
    end
end