What is it exactly you do not succeed to do ?
ok, I think this video gave me hint regarding the Production Files:
But, I am still a little bit confused:
Are these files are only guidelines, or can I produce the app assets from them?
If I am going to design my own glyphs, then in which format should I save a glyph?
They are pretty much just useful for prototyping design. Can you then slice and dice things for use in apps? Sure. But, you'll have to be careful. Namely, if you're going to stay in Photoshop, you'll end up with bitmap-based images. Thus, prepare to have to save various sized versions (currently 1x, 2x and 3x).
Personally, I use Adobe Illustrator for all my graphical asset needs. 99% of what I drag into .xcassets are PDF (vector-based images). I've done this since 2004 where OS X was supposed to have resolution independence. Much of the assets used in the iOS flavors of those older apps relied on the original Illustrator artwork.
Typically, I use a single PDF to drive iPhone and iPad artwork. Or, as needed, I use a single PDF for iPhone and a larger version for iPad. My Illustrator files always have the largest representation. Though in some cases, I did start with a smaller version, then upscaled.
Tip: Sometimes using a single image then downscaling can leave things looking bad. Mainly when straight lines no longer fall on pixel boundaries. So I pay attention in the original Illustrator files to have things be on pixel boundaries. And, if possible, at least on boundaries that are multiples of 4, 8, etc.
There are of course cases to use bitmap images. For those, I still start with as much as possible in Illustrator, then switch to Photoshop to do the necessary modifications.