VisualEditor is turned off for users of older web browsers. Also, it is currently not available to unregistered users. If you don't want to use VisualEditor on other browsers, for whatever reason, this page documents ways of avoiding VisualEditor and how to turn VisualEditor off.
One simple way to avoid VisualEditor is to click the tab "Edit source", instead of the tab "Edit", if you are going to edit an entire article or a User page.
If you want to edit a section of a page with the old wikitext editor, you need to hover the mouse pointer over the "edit" link to the right of the section name (or over the section name itself), then click "edit source" when that link appears.
This approach keeps open the possibility - deliberate or accidental - of editing in VisualEditor. If you absolutely don't want that, for at least a period of time, then see the options below.
The official opt-out
Access to VisualEditor is handled by user preferences on the English Wikipedia. To remove your access to VisualEditor, go to the Editing section of Special:Preferences and check "Temporarily disable the visual editor while it is in beta".
Options for IP users
VisualEditor is not currently available to unregistered or logged-out users at the English Wikipedia. However, it is possible to access VisualEditor by manually editing the URL. To do so, append
?veaction=edit to the end of the page name. For example, change https://en.wikipedia.org/wiki/Special:Random to https://en.wikipedia.org/wiki/Special:Random?veaction=edit to open a random page in VisualEditor.
At the moment, VisualEditor is turned off for users of Internet Explorer 9 and earlier. There are advantages and disadvantages to using IE as a browser, but if you're an anonymous editor who doesn't mind the disadvantages, and are using Windows, one option is to edit Wikipedia using an older version of Internet Explorer – you won't be offered the opportunity to edit with VisualEditor.
At some point, IE 9 will in fact be supported by VisualEditor. When that happens, you can check back here for more alternatives. Or you can use an even older IE version (8 or earlier) to edit Wikipedia - older versions will not ever be supported by VisualEditor.
Other (less-used) browsers may also not be supported by VisualEditor, now or in the future. You'll need to check each, individually, to see if the "Edit source" tab is visible on a Wikipedia article; if it is, then there will be an "Edit" tab to use VisualEditor, and the browser is supported by VisualEditor.