Sculpting
The sculpting menu allows you to define the general shape of a rock and then a rock will be generated. Start by pressing 'new'. This will create a 'sculpture in progress' in your scene with 1 sculpture point.
Next press 'add shape' to add more sculpture points.
Move the sculpting points in a certain shape and then press 'generate', this will generate a rock in the general shape that you created.
Don't forget to add a name to the sculpture and press save.