blogger: hiding content

You can show some content when you are logged in by wrapping the content in a span with class 'item-control blog-admin'. The content will still be visible in the source so do not use this for secrets. (via bloggingtips)

hiding the navbar

In the css section of the template add

#navbar
{
display: none;
}

admin section

You can modify the template or add a html widget.
To modify the template find the sidebar section

<b:section class='sidebar' id='sidebar' preferred='yes'>

Before this line add

<p style='text-align: right;'><span class='item-control blog-admin'><a href='http://www.blogger.com/post-create.g?blogID=your blogID'>new</a> | <a href='http://www.blogger.com/logout.g'>logout</a> |</span> <a href='http://www.blogger.com/home'>dashboard</a></p>

When using a widget, donot modify the template but paste the code as widget content.

You can find the url's and your blogID by entering the dashboard and observe the address bar.

The links for new and logout are invisible when not logged in. The link to the dashboard is always visible and will bring you to the login screen when not logged in.