How am I supposed to use Opera 10 spell check feature?

"Quick answer to what it is supposed to do. The spell checker is underlining misspelled words in red, a bit like you can see on word processors.

It won't popup a ""check mistakes and replace them"" dialog. However, when you will have a misspelled word, right clicking on it will show propositions of correctly spelled words in the context menu.

If you have several dictionaries, you will be able to switch which dictionary is active, at the bottom of this context menu.

Edit: More details on adding dictionaries can be found on Opera's site."

Obvious question - have you selected "Check Spelling" on the context menu? It's an option rather than an action and should have a tick (check mark) next to it if spell checking is enabled.