Arranging Posts on page

I am using wp 2.3.2, First im not sure I have the terminology correct but I need to rearrange the Posts? Topics that appear on the main part of the page. The page was originaly built with a Welcome comment, with other topics shown below, I then went and added two more Topics? which moved the “Welcome” topic down to third place.

I am just learning css, can anyone send me the code to rearrange the topics putting welcome first, along with the location of the file I need to alter.

Please respond if you need more info.

Thanks