By default the spell check feature is enabled in the Velaro agent desktop application when you install it.  To verify this please do the following:

1. Select Tools -> Options in the agent desktop
2. In the General tab expand the section for 'Spell Checking'
3. Select the check box for 'Spell checking enabled'
4. Select the radio button for 'Automatic' this way the application will automatically underline in red words that it thinks are misspelled
5. Select 'Apply'
6. Select 'OK'

If the spell checking is enabled verify the dictionary in use.  For more information on adding new dictionaries to the Velaro application see this article.
http://kb.velaro.com/KnowledgebaseArticle10133.aspx