Except for articles with strong national ties, the English Wikipedia has no preference for American, British, or other forms of English as long as usage is consistent throughout the article. In most cases, articles should stay in the dialect that currently predominates and should not be converted just for the sake of conversion. Any inter-dialect conversion therefore requires glancing at the whole article to be able to determine if, for instance, flavor, color, meter, or defense (or flavour, colour, metre, or defence) should be converted. Another approach is to try to avoid dialects by using words that are English universals.
Caution is needed when changing dialects and it takes some experience to avoid pitfalls. It is easy to make over- or under-generalizations. For instance, the endings "-ize" and "-ization" are acceptable in both British and American English. So although the suffix "-ise" is more common in Commonwealth usage than "-ize", both spellings are correct. Regardless, the use of "-ize"/"-ise" should remain consistent throughout a page.
Typo team members make many edits. It is always a good idea to give an edit summary after each of your edits, describing the change you made (see Help:Edit summary). If you made many fixes, you might say "spelling fixes" or "spelling cleanup". If the number of edits was small, you might list the exact words you fixed, such as "spelling Mississippi". You can also specify the exact change you made as with "spelling: lense → lens". Spelling fixes are generally marked as minor edits.
Additionally, you could simultaneously promote our project in the edit summary with a small reference like "typo corrections [[Wikipedia:Typo Team]]" or "spelling Monday [[WP:TYPO]]". The shortcut WP:TYPO links to this project page.
Edit summaries are important and other editors value them when scanning the article history. Edit summary histories are also sometimes considered during user requests for Wikipedia adminship; so, making valuable edit summaries is a good habit to form.
Recent versions of all major web browsers, including Mozilla Firefox, Google Chrome, Safari, Microsoft Edge, Internet Explorer, Opera, and Konqueror have built-in spell-checking. If you have a mouse with multiple buttons, usually a right-click over a misspelled word will offer suggested corrections. Remember that suggestions and the flagging of words as misspelled are not always accurate, and you'll need to read the context carefully.
For Firefox, additional spell-check dictionaries, such as British, American, Canadian, and Australian English, are easily installed via "Add Ons" or via a right-click "Languages" in an HTML form.
You can also search the page (including the edit window) for specific text, usually with Ctrl+f (⌘+f on Mac) or from the Edit menu.
Several browser extensions are available to check usage and grammar. Be aware that these extensions typically send the text you are editing to an external web site, which has privacy implications, especially if you use the same browser for sites other than Wikipedia. Some of these also have web demos you can copy-and-paste text into, if you don't want to install a browser extension.
It is possible to select text in the edit box (up to a whole article), then copy and paste it into a local program, edit it, and copy and paste back again. For example, this may simplify alphabetical sorting of list items. However, this depends upon the character set being supported; for example, copying into a standard installation of LibreOffice Writer is likely to be successful, but Windows Notepad is likely to corrupt characters, particularly non-English ones. This will not cause trouble so long as you preview and/or compare the pasted-back text with the original before saving. A quick once-and-for-all check that an editing program is suitable is to copy a page with, say, Chinese characters to the local application, maybe change one letter, save locally and re-open, copy back to the WP edit page, and check changes.
The following online tools can be used if you are unsure of how a word is spelled.
If you want, you can make a typo correction pledge on the pledges page.
You can show your support by discussing your work completed at the works completed page.
If you feel like someone has done exceptional work, you can reward them with one of these.
There are also some "ad"-style banner images to promote the Typo Team located at Wikipedia:Typo Team/ads.