Q: Is Spell-check functionality available?

A: Yes.

Q: In which fields is spell-check functionality available?

A: It's only available within two types of fields.  Multi-line Text and Rich Text fields, such as Address, and Description fields on Activities, Emails, Cases, Notes etc.

Q: How do I activate the spell-check?

A: You shouldn't need to activate the spell-check.  Any typos will be underlined with a red squiggle.  To display the alternative spellings simply right-click the mouse, or hold down the Ctrl key on your keyboard, and right-click.  

NOTE: This functionality is controlled by the web browser you're using, not Workbooks, which can differ between web browsers. Some web browsers do not require the Ctrl key to be pressed, but some do.