Help:Preferences
Preferences are settings made by a logged-in user that control that user's account and various aspects of the user's viewing and editing environment.
To access the preferences screen (having logged on), click "My preferences" (at the top of every page with the default skin), or navigate to Special:Preferences.
Along the top of the preferences screen are a number of tabs, which you can click in order to access various groups of settings. Depending on your screen size, you might wish to adjust the "Thumbnail size" (under "Appearance/Files"); this affects the default size at which many images in articles will be displayed. Remember to click "Save" after making changes.
Each Wikimedia wiki, including each language edition of Wikipedia, has separate preference settings. Some details are different at the English Wikipedia. For example, the option "E-mail me when a page on my watchlist is changed" is disabled for performance reasons.
It is not recommended to select "en-GB - British English" at the language option in preferences. Many interface messages have been customized at the English Wikipedia but only for the default selection "en - English". The language option only affects interface messages and not article text.
[edit] Detailed help
For detailed information about available preference settings, read Preferences Help at Meta.
(Note that preference settings made at Meta do not affect the English Wikipedia, so don't click "my preferences" on the Meta help page if you want to modify your preferences here.)
