Breath support is about managing the air pressure below your vocal cords. Your diaphragm has a very important role in the process of breath support.
When you breath in, the diaphragm lowers and air flows into your lungs. When you exhail without making sound, the diaphragm will relax and ‘pop up’, the air is flowing out of your lungs.
When you sing, the vocal cords close and will vibrate because of the airpressure under the vocal cords. Keep in mind that the airflow from the lungs during singing is much smaller than when exhailing without making sound. When you make no sound, your vocal cords are opened and the air can move out of your lungs freely.
Breath support is in a way about keeping the air in your lungs, creating the right amound of airpressure that is needed and keeping the small airflow going smoothly.
Joyce DiDonato gives a lot of masterclasses. Although she says she is not a voice teacher, she knows exactly how to explain how singing with breath support could/should feel like.
In this great video she uses the metaphor of tentpoles to help tenor Nicolas Darmanin to improve his breathing and breath support.
There are many ways to train your breathing skills.
Here are some:
A good way to learn how your diaphragm works is to sit reclined (slouching) with your arms crossed.
Just sit for a while and feel how your arms move up as you breathe in and move down as you breathe out.
Now breathe in and sing a tone. You will feel that while singing your arms will not go all the way down
as they did when you were just breathing out. This is because the diaphragm becomes active as soon
as you start singing. It wil stay lower in order to control the airflow.
When your arms move the same while singing as they did while breathing out, you will probably make a breathy sound. No breath control results in a poor sound.
Famous opera singer Montserrat Caballé helps a lot of singers to improve their breathing. Take a look at the video about her teaching a soprano how to prepare her breath support for a high note.
More exercises to improve your breath control:
The “liptrill” , to train your breath support and relax your jaw and throat.