For a spec about a browser feature, "getting it" can mean a few different things.
1. Understanding the purpose of the feature ("why/when would I use this?")
2. Understanding how to implement the feature
3. Understanding how to use the feature
4. Understanding the feature's "corner cases" (surprising implications, cases where it doesn't do what you'd expect, etc.)
5. Understanding why the feature works the way it does (instead of some other way)
Most of the web specs really only explain how to implement a feature, and even then, they're not great at that, because they do such a poor job at explaining the purpose of the feature.
Assuming that you, like most of us, aren't working on implementing a browser, that means that web specs are mostly unhelpful to you. It's almost completely beyond the purpose of a spec to teach you how to use a feature, what its corner cases would be (which are often unknown at the time a spec was written), and why the specification says what it says.
This is an area where the web spec community has made some improvements in recent years. Nowadays, it's understood that new proposed specifications shouldn't just provide a specification, but also a separate "explainer" document to explain the purpose of the feature, and also persuade the other browser vendors to implement the feature. ("This will be really cool, and here's why…")
At a minimum, specs nowadays often include a non-normative "Motivation" section, as the CSS Nesting spec does. https://www.w3.org/TR/css-nesting-1/ I you'll find that you can "get" that spec much better than you can the CSS OM spec https://www.w3.org/TR/cssom-1/ which is old enough to buy alcohol and doesn't include a "Motivation" section.
1. Understanding the purpose of the feature ("why/when would I use this?")
2. Understanding how to implement the feature
3. Understanding how to use the feature
4. Understanding the feature's "corner cases" (surprising implications, cases where it doesn't do what you'd expect, etc.)
5. Understanding why the feature works the way it does (instead of some other way)
Most of the web specs really only explain how to implement a feature, and even then, they're not great at that, because they do such a poor job at explaining the purpose of the feature.
Assuming that you, like most of us, aren't working on implementing a browser, that means that web specs are mostly unhelpful to you. It's almost completely beyond the purpose of a spec to teach you how to use a feature, what its corner cases would be (which are often unknown at the time a spec was written), and why the specification says what it says.
This is an area where the web spec community has made some improvements in recent years. Nowadays, it's understood that new proposed specifications shouldn't just provide a specification, but also a separate "explainer" document to explain the purpose of the feature, and also persuade the other browser vendors to implement the feature. ("This will be really cool, and here's why…")
At a minimum, specs nowadays often include a non-normative "Motivation" section, as the CSS Nesting spec does. https://www.w3.org/TR/css-nesting-1/ I you'll find that you can "get" that spec much better than you can the CSS OM spec https://www.w3.org/TR/cssom-1/ which is old enough to buy alcohol and doesn't include a "Motivation" section.
You can often find explainer docs linked off of https://chromestatus.com/ e.g. https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/... I think you'll find that explainers are 10000% better for learning features than specs are. (They typically even discuss #3, #4, and #5, as they typically discuss alternative rejected approaches.)