Haha... anything one wishes it to be
Yoga is a practice that anyone can benefit from. It doesn't matter your age, gender or level of physical activity. Everyone can get something out of yoga - and fall in love with it!
As with anything, you will get out of it what you put in to it. If you want to learn more about yoga and yourself, then go for it. At the end of the course, you will be able to join a class as a more knowledgeable student. And if you want to teach yoga, then take your certification course so that you can pass this wonderful practice onto others.
Yoga teacher training gives the opportunity for students to deepen their practice and gain a better understanding of yoga through self-study and group discussions. You will get the chance to work on your teaching skills under the close supervision of experienced teachers who have gone through the same process themselves.