Earlier we took a look at how to add Custom Web Part Pages to your SharePoint sites.  You can also create custom pages within SharePoint Designer.  To get started, open your SharePoint site in SPD and choose to create a new ASPX page:

An ASPX page is an ASP.NET page.  When the page loads you can see that it is essentially a blank canvas.  If we switch to code view, you can see it contains the bare essentials required by an ASPX page:

Now that we have our canvas, lets add some SharePoint functionality to this page.  From the Insert menu, select SharePoint Controls and choose to insert a new Web Part Zone:

By inserting  a Web Part Zone, SharePoint designer also adds an SPWebPartManager which is required to support Web Parts on a page.  We now have a working Web Part Zone for our page:

All we have left to do is save this page and view it in the browser:

Now, when you load the page you might be a little discouraged but don't worry!  Your page isn't really empty.  To see your Web Part Zone, however, you'll have to tell SharePoint that you want to edit the page.  You can do this by running some JavaScript from your address bar:

Here is the link you will need:  BLOCKED SCRIPTMSOTlPn_ShowToolPane('2')

Simply paste that JavaScript into the address bar and press enter to execute it.  (Big thanks to Todd for the shortcut!)

Now you should see a usable (if not exactly pretty) Web Part Page: