I'm not sure how to use the diaphram to sing. How can I get it working? I know it may sound dumb but I want to learn!
It doesn't sound dumb at all. It's great that you want to learn how to improve your singing, and it's even better that you're interested in opera. To make any significant improvement you will need to find a teacher, but let's see if I can give you some tips to get started…
Practice every day. It is better to warm up for 15 minutes, three different times during the day, than to spend 30 minutes straining to reach notes. That way each warm up almost acts as a new day's warm up. So you get three days of work in one day.
Using the diaphragm: When you breath you should work on making your rib cage expand. A lot of people only move their chest when breathing, you want to fill up your ribs and the area just above your stomach too. Think of your lungs as a balloon and you'll get the idea.
Don't strain your voice. The first thing that people do when they want to sing is force themselves to sing notes that they really can't reach (both high and low). Find the middle of your range and start from there.
Try singing a few notes at a piano. If you have piano skills, great. If not grab a friend who does. Play a single note and then try matching your voice. Listen carefully to what you are singing vs. what is being played. Try this on different vowels: e eh ah Listen CAREFULLY. Even better, have someone else listen to make sure you are singing the right pitch.
Next, warm up slowly. Don't start very high. In fact, it might actually be better to go down first. Start on middle C doing a five note scale (C => G and then back down) and then go down to B, B-flat, A, you get the idea. Try to connect your pitches through air. You don't want to swoop, instead try to keep a very steady flow of air coming out of your mouth. For example: If you take a big breath and then exhale you will notice that it is very smooth, the air is steady, it doesn't sound like a scratched CD. Apply this to your exercises.
Now you can go up. Keep in mind the same things: don't swoop, steady air, don't strain. As you repeat this throughout the day you will notice that your voice will get stronger, as will your range.
I don't know if you know solfedge, but if you do then these exercises are good. If you don't, maybe a friend can explain: (note: (do) = high do)
do mi sol mi do
do mi sol (do) sol mi do
do sol do
do (do) do
do (low-sol) do
Now apply the skills you have learned in these exercises to the songs you are singing.
Listen to operas. You can learn a lot by just hearing what the experts do. Get exposure to all different styles from Verdi to Wagner (I'm not so much of a Wagner fan myself, but to each his own.) to modern day opera. See what you like and don't like.
When you find a teacher sign right up. If you don't already know who you want to study with then go to your local music store and ask. They usually have a record of all of the private teachers in the area. Be prepared to call multiple people because by this time of year many teachers have all of the students they can handle.
Good luck and let me know how it goes!