Popular music vocals is pop, rock, folk, country, R&B etc but not music theatre or opera. You can learn to sing just for fun and wellbeing, or study for a qualification such as an LCM popular music vocals exam or improve your skills to sing with your band. Popular music vocals includes music theory however, this approach is largely away from printed sheet music so you don't have to be a great music reader to explore your talent.
Popular music vocals is not suitable for young children, it is suitable for people from age 10 upwards and adults. It is an area of music that is particularly popular with adults.