If you grouped layers in the PSD design template not quite well we will try to do it for you. Service of PSD to CSS Conversion will group layers into columns and rows and turn them into separate div blocks. Grouping is made for layers into each Layer Group in the Photoshop file.
But the fact we are doing an automatic groping of layers does not mean that we are doing it in the best way. We can't predict your intentions for different layers perfectly. That's why we recommend you to group layers in your PSD template by yourself. Unite layers into Layer Groups in the logical way (mark out columns, rows, etc). The better you group layers the better HTML CSS markup you will get. Thus, in the first place that's you who are responsible for the quality of converted HTML and CSS!
Photoshop offers different color blending modes for layers. For the Psd to Html Conversion service you should use only 'Normal' blending mode. HTML and CSS simply do not support other blending modes. If your design uses blending modes other than 'Normal' then, please, merge such layers with the layers underneath them.