Help converting an existing design to GetSimple

[Joeclef]

Hi all,
I have a small website that I'm working on(www.aucap.org.ht), I have already started it in plain HTML/CSS now I would like to use GetSimple because I think this will make it easier to update the site.But I don't know how to convert the existing (CSS) design into GetSimple. Can anybody help me with that issue. This the first website that I'm designing, so I'm new to the field. If you have any suggestions on how to improve my design please let me know. Thanks