On question 1a should I put the date I first time entered USA or during the tax year.
I was a student during 2008 to 2010. I fist entered usa in 08/09/2008 and after summer vacation in 2009 I entered usa in 08/24/2009.
What should I put for 2010 form 8843?

Put the date you first entered the U.S. under your current F-1 or J-1 visa,so put 08/09/2008.