How to make a speed block?

I'm not going to give you the answers straight out, but use the Touched event and Walkspeed in Humanoid.

Or you can just use this http://wiki.roblox.com/index.php?title=API:Class/Humanoid/WalkSpeed

If you can't figure that out, I suggest reading

http://wiki.roblox.com/index.php?title=Intro_to_Scripting

Place this inside the speed block

local function touched(hit)
    local humanoid = hit.Parent:findFirstChild("Humanoid")

    if humanoid ~= nil then
        humanoid.WalkSpeed = 50 --Change 50 to how fast you want the player to go
        print("Worked!")
    end
end

script.Parent.Touched:connect(touched)

So, first off, place down a part, put a script in that part, and put this script in.

p = script.Parent

function powerup()
    game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 1337 
end

p.Touched:connect(powerup)