>>2625560Those are pretty good tutorials.
The gist of it is that the lowest zone is pure black, the highest zone is pure white, and each zone is ideally separated by a full stop of exposure. Metering from a spot always tries to get that spot into what would be called "zone V," or the intermediary, so instead, you should consciously place different elements in different "zones" of exposure and shoot based on that. It's the best way to avoid unnecessarily blown out highlights and drenched shadows.
On black and white film, you have 0-X. On color and digital, only zones III-VII exist.