I'd start off by copying header.php from twentyeleven into the child theme. Then look for this:
<hgroup>
<h1 id="site-title"><span><a href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></span></h1>
<h2 id="site-description"><?php bloginfo( 'description' ); ?></h2>
</hgroup>
Adding an <img> element for your logo immediately inside the <hgroup> element would be a good start. I'd give the <img> element an id of logo if that id isn't already being used.
After that, you'll probably want to add a style rule to your child theme's style.css file, like this:
hgroup img#logo {
float: left;
}
Once you've done that, you can look at it again to see if there's anything else you want to do to style things a bit more.
HTH
PAE