How can I make a script run again?

Like if I do a = Instance.New("Part") How do I make it run again if perhaps, someone clicked a button. I am pretty new to scripting so I need some help.

tempestatem is correct, but he forgot a few things. here's a lil more Accurate Script

while true do
wait(5) --Waits 5 Seconds
a = Instance.new('Part', game.Workspace) --He said Part.Parent, he didn't Define Part, it's 'a' but I made it in 1 line
end

And an OnTouch Script

script.Parent.Touched:connect(function()
a = Instance.new('Part', game.Workspace)
end) --')' is expected to close the connect:(function) at the end