Lesson 2-1-1 - Low D
Low D is the lowest conventional note on a Soprano D whistle.
It's made by covering all six holes completely, and blowing softly into the whistle.
Low D is one of the tougher simple notes of the lower octave on a tin whistle. If you're starting out, I'd suggest trying Low B first, as the breath control required for Low D means that you're best off leaving it until you've learned B, A, G, F#, and E.