I hope you don't interpret this thread as cruel or unhelpful, but there's a certain amount of truth in the answers here: you're jumping in the deep end without knowing too much about the program, which makes it difficult to explain the answers to your questions, too. You're asking about the finer points of the chemistry of combustion before you've put fuel in your car. If you don't need to use something, you can safely ignore it: there are a lot of plugins, and several are tailored to solving very specific problems, which many users are unlikely to come across.
Instead of trying to figure out everything in one go, it would probably be best to go about making the games you want to make, then when you come across a specific problem, ask what the best way to solve that is.
For example, you may be off making your game, and you need to attach certain pairs of objects together. Due to the particular circumstances, 'natural' pairing (i.e. equal numbers of both objects) doesn't work, and the container system doesn't help. If you then ask how to do it and the answer is "Try the Object Pairer plugin", it'll make a lot more sense. If you just ask "What is the Object Pairer plugin for?" without having much experience with the program, it's hard to know what to say: "Umm, well... things normally pair up together automatically... usually if there's something wrong with that you can use the container system (which is useful for a whole load of other things too)... in certain specific situations outside of that, Object Pairer is useful." That's a bit vague and not really helpful, and you won't get the "Ooooh!" moment of understanding you'd get when the answer solves an actual problem you're having. That's probably why the answers you get to this type of question are, well, terse.
Also, being a part-time volunteer-developed open-source project, the documentation is sketchy. It's a well-known drawback of Construct, unfortunately. I'm kind of going nuts with university work right now, so I don't have much time to fix any of these problems - most people get by with forum searches, practice and using what is available on the wiki. I've asked in the past for users with experience to help flesh out the wiki, but it hasn't really seen a great deal of contributions, which isn't that surprising - it's hard work.
Some of the issues you pointed out are also simply badly designed parts of Construct. These should be fixed in the next version - Construct 2 - and should also include a better help system, but that's somewhere just over the horizon, don't depend on it turning up any time soon.
Still, I hope that helps, that you enjoy using Construct, and that you get everything figured out - it's just it looks like you're trying to go a little too fast. Please do feel free to ask more questions, maybe just aim them at what you're currently doing, then we can help you better too