A-E-I-O-U
Focus in this exercise on what you need to do with your mouth and tongue to produce your vowels.
The goal of this exercise is to stay in your original voice, your speaking voice, for as long as possible. What do you need to do to maintain your original sound?
One of the things that you need is a good breath support!
And don't force anything but go to your falsetto when you feel that you're gonna push the notes.