It's 100% true. When you lift weights, you actually break down your muscles. It provides a stimulus to your body to rebuild them bigger and stronger.
It's kind of like this
'you go to the gym and break down your muscles. Your body then goes 'wow, we were not ready for that. We just got the crap beaten out of us. We need to rebuild these muscles bigger and stronger to make sure we are ready for that next time!'
Most people thrive on weight training 4-5 days per week. Get in the gym, hit it hard and then let the muscle repair and grow.