Freediving is diving without tanks, on one breath, relying on technique and a surprisingly trainable body. It looks superhuman and is mostly about relaxation. The biggest gains come not from bigger lungs but from staying calm and efficient, which anyone can learn.
A beginner course teaches breath-hold technique, equalisation and safety, usually in a pool and then open water. Most people are astonished how quickly their breath-hold improves once the panic goes and the technique arrives. It is as much a head game as a physical one.
The instructors on adventuro run beginner courses through to deeper training, always with the safety practices that make freediving sensible. You never freedive alone, and good instruction is the difference between a calm hobby and a bad idea.