Hi Roman - usually sculptured surfaces like that are created by creating some profile curves and using either the Sweep or Network tools to create surfaces from those curves.

So the starting point though is to create some curves that follow the outline profiles of the surfaces that you wish to create.

To create curves that flow in 3 dimensions you can do stuff like start by drawing a profile in the top view, then turn on control points with Edit > show points, and then move some of those points upwards in one of the side elevation views.

It will take some practice to get comfortable with doing this - that kind of highly sculptured shape with stuff kind of swooping around in 3d tends to be more difficult to model than things that are more mechanical in nature.

- Michael