Cannot understand example in TryFSharp.org

i do not understand this example from tryfshart.org

let twoTest test =
    test 2

twoTest (fun x -> x < 0)

http://www.tryfsharp.org/Learn/getting-started#fun-functional

what does the line "test 2" mean?

how would i use this?

how can i test it? where can i put a printf statement to see the output?

thx