The ScreenSteps desktop editor has spell check built in. You can either check spelling as a one-time event, or you can check spelling as you type.
Check Spelling (one-time check)
Click on Edit > Spelling > Check Spelling
Check Spelling While Typing
You can also turn on spellcheck so that it checks spelling as you type, and underlines misspelled words.
Click Edit > Spelling > Check Spelling While Typing.