The four-letter suffixes correspond to the OpenType features with the same tags, in case you wondered. The one without a suffix is the isolated shape. The glyphs we are looking for are all called behDotless-ar, indicating the dotless beh of the Arabic script, and the positional variants will have additional dot suffixes. And that is what we refer to as a ‘basic shape’. Then you end up with a shape that you can reuse for the teh and the peh, some positional forms of it even for the yeh and the noon.
Though, imagine for a moment that you take the beh, but leave out its dot.
If you can read Arabic, you will probably say, ‘Wait a minute, there is no beh without a dot, the beh always has a dot underneath.’ And you are right, of course. Of course, you can start with anything, but the Basic Shapes are indeed a good place to start because it contains shapes that are reused a lot in other glyphs. Okay, so let’s select Arabic > Basic Shapes in the sidebar, so Font view will only display relevant glyphs. As long as you are working inside Glyphs though, you will not need to worry about it. At export, the names will be converted into so-called ‘production names’ the way they are expected in an OTF. The -ar suffix, as you probably have guessed already, indicates that the glyph belongs to the Arabic script. You will notice that Glyphs uses human-readable names like alef-ar as opposed to ‘uni0627’ or ‘afii57415’.
