Developing a simple DotNetNuke skin is pretty easy, and just requires a few items...
So lets create a new file for our skin, and call it SimpleSkin.htm. To allow content to be automatically inserted into your skin by dotnetnuke we must add a tag called contentpane ~ add this line to your skin:
<div id="ContentPane" runat="server" />
Note that there must be something, a div or a span, or a td, named contentpane ~ it is required. any other content areas you add after this one are optional and can have any name.
Now we need a control panel so that we can access the page editing functions, add this line to the top of your skin file:
<div id="ControlPanel" runat="server" />
Note that this panel must also be named correctly in order to work.
And now lets add login and register to our skin, add this between the two items already in your skin:
<div>[LOGIN] [USER]</div>
Thats it! we dont need anything else for our first simple skin! Bringing it all together we end up with a file that contains these three lines in this order:
<div id="ControlPanel" runat="server" />
<div>[LOGIN] [USER]</div>
<div id="ContentPane" runat="server" />
Now to use this skin, first copy it to your website folder, under /portals/_default/skins/simpleskin/simpleskin.htm. Use windows explorer to copy the files to a website on your own pc, or use ftp to copy the files to a hosted website.
Go to your site, and login as admin or host. Now browse to the admin menu, skins page. Select simpleskin from the drop down list, and then click the "parse skin package" button. Your skin is now installed and ready to use.
Now that you have created your first simple skin, go out and read up about how to layout web pages using divs and css. Hey, psst its even ok to use tables to layout a page if you quite arent sure what you are doing.
Once you have made a more complex layout, just take every part of your layout where content should go and add <div id="LeftPane" runat="server" />, or "rightpane", or "toppane", or any panel name you like... start small and build on a simple skin for best results, and soon you will know how to develop DotNetNuke skins too.