How do I make it the players damaged when it touches a certain block ?

Put in a regular script inside the brick.

script.Parent.OnTouched:connect(function(p)
    if p.Parent.Humanoid~=nil then
        p.Parent.Humanoid.Health=p.Parent.Humanoid.Health-20 -- Can be any damage you want
    end
end)

try this

script.Parent.Touched:connect(function(hit)
human = hit.Parent:FindFirstChild("Humanoid")
if human then
human:TakeDamage(5)
end
end)

Thanks both of you guys for your scripts this has also teached me some scripting