If I might clarify, your question appears to be: "What can I use to understand mathematics if a major resource like Wikipedia makes no sense?" Keep in mind that even a person who has mastered a concept had to begin with a period of not understanding it, and then go through a learning process, albeit one that almost never involved learning much from Wikipedia.
Having spent a lot of time studying things that are described quite atrociously on Wikipedia, I can assure you that even when one understands the concepts quite well, it is difficult to make sense of what was going through the minds of one or more authors/editors on Wikipedia. It is not uncommon to see mathematical and statistical concepts mutilated by a bunch of people with a very rough grasp of the concepts or in pursuit of advancing yet another field's weak grasp of the fundamental concept. (I would say more, but it is hard to do so without sounding unduly pessimistic about the efforts of Wikipedians, especially those from certain other disciplines.)
On a more constructive note, the best references are typically those textbooks edited by publishers with a strong track record of editing and publishing good works in the given field. Authors and editors in such cases have a reputation among their peers for the quality of their scholarship and rigor, and a series of successive editions usually indicates acceptance by other teachers and researchers.
There are many levels of quality between that level and Wikipedia. If the print editions are not available, using Amazon's "Search inside the book" or Google Books may be the best alternatives.
For other web-accessible references, you may find that review articles or manuals for non-specialist practitioners are most useful. An example of this is the statistics handbook published by NIST.
You may need to synthesize your own understanding by way of looking for articles in Google Scholar. For instance you could query ["a point process is a"] and examine the definitions offered in various articles. Alternatively, a web search like ["point process" pdf site:edu] will turn up lecture notes, slides, and tutorials. The first result for that query appears to be "An introduction to point processes". The key idea is that one should search for terms that either tend to appear or may appear in the appropriate level of material that would define and introduce the concept, whether or not the phrasing was intended to denote that the reference has some relevant exposition (e.g. a journal article may define something in a useful way, even if it isn't intended to be an introductory text).
It is impossible to push against the bad edits on Wikipedia: for certain articles, the number of bad editors exceeds the number of people who can tolerate fixing their errors.