Maybe you can tell us what you want to render in your sidebar? Is it content from the same page?
Anyway, your html markup should consist of two floating divs, something like:
<div class="wrapper">
<div class="content-area">
<?php echo $page->text()->kirbytext() ?>
</div>
<div class="sidebar">
<?php echo $page->somefield()->kirbytext() ?>
<!-- or whatever you want to output here -->
</div>
</div>
CSS
.wrapper:after {
display: table;
content: " ";
}
.content-area {
width: 60%;
float: left;
}
.sidebar {
width: 40%;
float: left;
}