So, you want to compare two versions of a doc (probably one circulated by you, and the other you received revised by somebody). Here's how to get it done:
1) Open the original document.
2) Go to menu 'Tools' > 'Compare and Merge Documents'
3) In the 'Open' dialog, point to the newer version of the document, and click open.
4) And you are done.
MS Word will show you the changes (like something new inserted, deleted, etc) with appropriate coloring.