Hiya! And welcome to Wiki!#
Anyone can contribute, even anonymously. Yes, you can delete what other people said, and even delete whole pages, but surprisingly, wiki does work.
When editing, you can easily create (and you should create) hyperlinks by just putting the word in square brackets, [like this]. If the page you are referring to does not exist, the resulting page will show the name underlined, with a following question mark. Like this: ThisPageDoesNotExist. (Please don't foil this example by creating that page...)
WikiNames that contain spaces or underscores are crushed together and capitalized, so that [This is a link] becomes [ThisIsALink].
Wiki is and should be simple. This is why there is no need for complex HTML. You can get some effects, such as bold text and italics, but nothing very complex. Layout is the problem of the Wiki itself. There is more information in TextFormattingRules.