Is there anywhere where a theme how to can be found on the forum?
preferably technobabble free.
It's code. That means technobabble, to some extent.
The sprites aren't hard to understand if you understand how css positioning works. The numbers in px or % are used to set X-axis and Y-axis positioning. In the case of single images for each bit, those numbers are usually 0 or 100%. In the case of sprites (compound images) they can be set to any required value.
You can also set them to any required value for single images if you want to, for instance if you would rather tweak the position of an icon via css instead of making a new image, but it's not often done in practice.
If you want to do theming you really need to learn at least basic css anyway. There's no way around that. In fact, with the use of non-tabular layout in large parts of 2.0 you really need to know a fair amount of css if you want to change anything substantial.
There are basic theme tutorials but I can't recall how detailed they are or where they are. Not to boast excessively, but it's been quite a while since I needed one so I haven't bothered looking.