Hi. smile Im an operatic tenor. Just some pointers.
Your diaphragm is above your stomach. If you lay down and sing on your back, you can feel your diaphragm push, thats where you want to sing from when you are standing up. It takes a long time and a lot of practice to develop it. While you are standing you have to conciously try and sing from there while standing with a straight back. At first it hurts and is hard to isolate just the diaphragm but after about 2 30-minute sessions a day of singing from there in about 2 weeks you should see a noticable ease in using it. After you figure out how to use the diaphragm well you want to focus on raising your soft pallette (its like right by the tonsill in the back of your throat) .... if you like drop the back of your jaw and then kind of try to breathe through the back of your eyes (I know that sounds weird, but what im saying is lower the back of your jaw and when you have your soft pallet up your eyes will feel just a tiny bit colder because there is more air circulating). If you get your diaphragm and your soft pallette mastered, then its all about just doing vocal excercises to develop a large range. I currently have 4 octives I can sing in including a whistle registry. Also if you have everything lined up correctly, such as diaphragm, with chest expanded, soft pallet raised and an open throat, when you sing you will hear something such as a wavey sound to the voice, thats called vibrato, and it happens naturally when everything is lined up, you cannot create vibrato, but when you get used to it you can control it to an extent. .... I hope these comments were helpfull for you.