The huge majority of people, and magicians, are not material-minded. The condition, or conditions (there are several forms), affects perceptions and understandings in a rather basic way. An example would probably be easiest.
Weft's material-mindedness surrounds cloth and thread. This is not because he's good at working with cloth; rather, he's good at working with cloth because he's found something that thinks like he does.
Understanding this distinction is essential to an understanding of material-mindedness in general.
It is extraordinarily improbable, and may well be impossible, to think convincingly like another person, even when there is not a gross neurophysiological difference in the way. Thus, any attempt to describe or imagine a material-minded person's thought process can only ever approach an educated guess. (But it's such fun.)
Weft understands things in terms of weave, folds and knots - metaphorical, but only just. To weave a spell, he would have to comprehend things in orderly rows and warps. He's not brilliant at this, which (from certain people's viewpoint) is a pity, as his methods would otherwise make a fascinating study.