How to get localplayers gui text?

You could have a RemoteFunction somewhere that both the server and client can see. (Workspace or ReplicatedStorage will do just fine)

On the client, you should do:

YourRemoteFunction.OnServerInvoke = function() --replace YourRemoteFunction with your RemoteFunction's location
    return MyGui.Text --replace MyGui with wherever your GUI is located
end

This will basically say, "Hey, when the server fires this RemoteFunction, I want to give it whatever is written in MyGui.Text."

Now, on the server, you can very simply do:

local Text = YourRemoteFunction:InvokeClient(playerToSendTo)
print(Text) --prints whatever they have in their text entry

Just replace playerToSendTo with the player you want to ask for the input and you should be good to go.