To create an ASM file, you first need a set of images that have been marked up.  More is good, but even a dozen can give a useful ASM.  However, it will be sensitive to individual images, and one more or less may have a large effect on the utility of the model.  Having got your images and templates in a folder:

1. Make a list of the files: Average -> Make average list

2. Set normalisation to 3 point: Average -> Shape normalisation

3. Build the ASM: PCA -> Build shape PCA (ASM).  It will first ask for where to save the asm file, e.g. male.asm.  It will then ask for your filelist from step 1.  You should then see it creating an average image; when it has finished a pop up appears, and there should be five files in the folder: the average image and its template, the asm file, a pca file and a txt file of eigenvectors.  This txt file is not needed for subsequent loading of an ASM into the program, the other four are.