Please take a look at the skinning document @ http://www.dotnetnuke.com/Resources/Documentation/DownloadableFiles/tabid/478/Default.aspx , it should get you started.
Alternatively just examine one of the existing skin containers e.g if you look at
\Website\Portals\_default\Containers\DNN-Blue\Image Header - Color Background.ascx
you'll see 2 table rows that look like
<TD valign="middle" nowrap><dnn:ICON runat="server" id="dnnICON" /></TD>
<TD valign="middle" width="100%" nowrap> <dnn:TITLE runat="server" id="dnnTITLE" /></TD>
These are the icon's and title, so you would simply update them as you would normal html i.e.
<TD valign="middle" nowrap><dnn:ICON runat="server" id="dnnICON" /></TD>
<TD valign="middle" width="100%" nowrap align="center"> <dnn:TITLE runat="server" id="dnnTITLE" /></TD>