Microsoft 2007 does not correct words spelt incorrectly!?

I have Microsoft word 2007 and it does not correct or underline the words that i have spelt incorrectly. i noticed this when i typed out something and printed and to only later find out when i was reading the doent that it was full of errors. i have tried browsing through options and that but still cannot seem to find a solution. any ideas please? your help is most appreciated! :)