Newcomers and those seeking an introduction to Ethereum may go to https://ethereum.org or https://github.com/ethereum/wiki/wiki.
Note that you can proofread while you read and learn about anything.
Please just edit the pages in the wiki directly as shown in the sidebar here: https://github.com/ethereum/wiki/wiki, rather than making pull requests.
Please only create an issue if you can't fix it by editing yourself, and only if it is related to the wiki. If it is a technical issue e.g. with web3 or JSON.RPC, geth, Mist (although note that Mist isn't really user-ready yet, so using alternatives like MyEtherWallet is recommended instead), etc., please post an issue in the repo for that project as well, and reference the issue that you create in this repo (by copying and pasting the link to the issue in this repo in a comment in the issue in the relevant project repo).
If you are translating an article, please create a new page and create the translation in that. Do not edit an existing article by translating it. Someone did this with the home wiki, changing the title, and this actually caused the home page to just direct to a list of pages in the wiki, and made it hard to find the edited home page as the title was changed to Arabic. So do not edit the title of an article.
If you have experience with editing on Wikipedia, then that will help with knowing how to edit this wiki, although the contribution rules are less strict. Referencing facts is a key writing and proofreading task, as well as checking that information is up-to-date (and updating it if otherwise), correcting grammar, typos, and spelling; and making the wiki comprehensive and easy to understand.
Other rules, such as a neutral point of view and no original research are desirable, but may be hard to maintain. Notability is less relevant.
