Apps are great to recommend a training and exercise plan, showing you different ways of working out etc. However I found that without having a professional by my side, especially in the beginning stages, it was impossible for me to know if I'm making mistakes in the way I carry out the exercises, wrong postures, incorrect movements or alignment of limbs. Once you learned to do them incorrectly, it can be very hard to correct this and have bad consequences for your health to a point where you can seriously hurt yourself. No app can do that for you.