How do you make it so when you touch an item, it displays a message?

~~~~~~~~~~~~~~~~~
local msgText = "You need a key to continue."
 
script.Parent.Touched:connect(function(hit)
    local findhum = hit.Parent:FindFirstChild("Humanoid")
    if findhum then
        local player = game.Players:GetPlayerFromCharacter(hit.Parent)
        local findm = player.PlayerGui:findFirstChild("msg")
        if not findm then
            local msg = Instance.new("Message", player.PlayerGui)
            msg.Text = msgText
            msg.Name = "msg"
            wait(5)
            msg:remove()
        end
    end
end)

~~~~~~~~~~~~~~~~~

It works, the message will display. You just forgot the part at the bottom. This might fix it!

local msgText = "You need a key to continue."

script.Parent.Touched:connect(function(hit)
    local findhum = hit.Parent:FindFirstChild("Humanoid")
    if findhum then
        local player = game.Players:GetPlayerFromCharacter(hit.Parent)
        local findm = player.PlayerGui:findFirstChild("msg")
        if not findm then
            local msg = Instance.new("Message", player.PlayerGui)
            msg.Text = msgText
            msg.Name = "msg"
            wait(5)
            msg:remove()
        end
    end
end

script.Parent.Touched:connect(onTouch)

Let me know if it doesn't work.

Your problem is most likely this

player.PlayerGui:findFirstChild("msg")

Find must be capitalized for this to work. If it doesn't then post the error you are getting in the output.