All three of the GH components have some level of 'macro nutrients' (NPK) in them. They are meant to be mixed proportionally to get the right levels.

The 'Grow' has mostly N.
The 'Bloom' has mostly P and K.
The 'Micro' has some N, plus a whole mess of micronutes.

When you mix them as directed for each stretch of your grow routine, they will make up to the correct NPK ratio for that part of the growing cycle.

Often a grower will also need a mineral supplement such as CalMag. Although calcium is not an NPK macronute, it is still required for growth, and if your tap water doesn't supply it, you will have to supplement.