bad argument #1 to 'sub' (string expected, got function)?

function text(txt)
    for i = 1, #txt do
	    script.Parent.Text.Text = string.sub(text, 1, i)
	    wait()
    end
end

text("yo gang")

I know whats wrong I just don't know a good way of fixing it

You are putting the function "text" under the parameters of string.sub. To fix this, simply change the parameters to "txt" instead.

Also, to get the length of a text, I believe you must do string.len(txt) rather than #txt, for "#" returns the number of values inside a table.

Thus, the code should look like this:

local function text(txt)
    for i = 1, string.len(txt) do
	    script.Parent.Text.Text = string.sub(txt, 1, i)
	    wait()
	end
end

text("yo gang")

Hope this helps! Message me with any problems you may have :)