What is the difference between exchange 2010 and exchange 2013?

Your question is not clear, are you asking from user perspective or administration or consultant. If you are administrator and currently looking to upgrade to2013, I advise you to wait as there are stability issues. Overview of comparison can be found in below link.   

http://office.microsoft.com/en-001/exchange/microsoft-exchange-server-version-comparison-email-server-FX.aspx