The spell checker automatically works as you type - enter your text, make a mistake and the typo is underlined. Tap on the typo to flag up alternate spellings from the context menu. And tap on the context menu to choose more spelling suggestions from the properties panel.

You can change the dictionary - the language of the spell checker, by choosing Document language from the Document properties panel and then choosing a language. This is useful if you have a document containing a mixture of languages. So I might have a document in English with a passage of German which I wish to spell check - just switch languages in the spell checker and it’s done. There is also a No language option. Apply if you don't want spelling checked - useful for example if you have some dummy 'Lorem ipsum' text in your document as a placeholder.

Two more features - Ignore word and Add to dictionary will come in a later update.

To see the document properties panel make sure you have nothing selected (click an empty part of the workspace or hit Esc on your keyboard) or via File > Document Properties.