Well to gain strength in your voice, in really simple terms, when you breathe in to sing or speak in a projected manner, you need to take quite a small breath in, and as you sing (or speak) a phrase, you leave the ribs where they are. You only let your ribs relax at the end of the phrase. This causes the diaphraghm to work and to provide a steady flow of air and what they call 'support' for the voice. A singing straw is a metal straw which you do your singing exercises through. Some have holes in so you can increase the pressure. But basically it's like humming with your lips very slightly apart. It creates some back pressure on your vocal cords and enables your voice to work without strain. Public speakers use them too sometimes.