Select Layout > Edit HTML > Edit Template

Copy below code before </head>

<style media='print' type='text/css'>
#navbar-iframe {display:none ; height:0px;visibility:hidden;}
.noprint {display: none;}
body {background:fff; color:000;}
a {text-decoration: underline; color:00f;}
}
</style>

Put <span class='noprint'>... </span> code where you don't want to print, e.g sidebar

<span class='noprint'>

<div id='sidebar-wrapper'>
<b:section class='sidebar' id='sidebar' preferred='yes'>
<b:widget id='Label1' locked='false' title='Label' type='Label'/>
<b:widget id='BlogArchive1' locked='false' title='Blog Archive' type='BlogArchive'/>
</b:section>
</div>

</span>

or in the blog post content

Select Posting > Edit Posts

<span class='noprint'>

Content that you don't want to print

</span>

Put below code in your post content (print link)

<span class='noprint'>
<div align="right"><a href="javascript:window.print()">Print</a></div>
</span>