Than - used for comparision,
        -  Comparitive, less than or more than 

<em>For Example - a. She is bigger than me.</em>
<em>                   b. I have more money than my sister.</em>

Then - Squence/time

<em>For Example - a.  I ate dinner then I cleaned up.</em>
<em>                   b. First I rented the movies then I watched all three  LOTRs back to back.</em>