Any help plz?

There are two possibilities for you here, seeing as how you aren't completely clear in your question:

1. You want the part to have 0.5 Transparency when someone enters the game. Easiest thing to do is go into the properties of your chosen part and change the 'transparency' to what you want it to be. No scripts needed.

or, 2) You want it so that when you touch a brick, it changes the transparency. You've had a go, but you'll need a function to activate the script:

function onTouch()
	script.Parent.Transparency = 0.5
end

script.Parent.Touched:connect(onTouch)

Make sure the script is inside the part you're wanting to be transparent.