Why Doesn't BodyVelocity move the player?

RicheeNektar is right: "Because the Velocity.(X/Y/Z) are READ only properties of the Velocity from the player that means you can only read their values and not set them. You need to set them with the Vector3.new()".

In addition, your script parented BodyVelocity to the player's character. It should be parented to one of the character's parts such as Torso. Try adding this:

new.Velocity = Vector3.new(0,150,150)
new.Parent = Character.Torso

Notice that you can access the BodyVelocity's Velocity property directly since you established that the variable "new" is the new BodyVelocity. You need not find the velocity with "Character.Vel" each time.

Because the Velocity.(X/Y/Z) are READ only properties of the Velocity from the player that means you can only read their values and not set them. You need to set them with the Vector3.new() function Try this:

script.Parent.MouseButton1Click:connect(function()
    Player = script.Parent.Parent.Parent.Parent.Parent
    Character = game.Workspace:FindFirstChild(Player.Name)
    if Character ~= nil then
        Hum = Character:FindFirstChild("Humanoid")
        if Hum ~= nil then
    Hum.Jump = true
    local new = Instance.new('BodyVelocity')
    new.Name = "Vel"
    new.Parent = Character
 Character.Vel.Velocity = Vector3.new(0,150,150)
wait(10)
new:Destroy()
        end
    end
end)