[Gmsh] How to create a boundary layer mesh around an airfoil with x layers...?

[Klaus Burkart]

Hello,
I don't understand how to create a boundary layer mesh, lets say with 20 layers, made up of prismatic cells around an airfoil. 

I need a mesh with y+ = 1 which means a wall distance of 0.000016 (first cell hight) to be able to get correct airfoil drag results.
Note: The airfoil is made up of a spline and a straight line at the trailing edge to correct a strange trailing edge shape and to be in line  with manufacturing process requirements
I don't get, the concept and required syntax of extrusion to create the boundary layer. Of course I looked at example 3 and in the manual etc. but I didn't get it.

How does it work?
Find attached the current status of my meshfile.
Regards,
Klaus

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