TwentyEleven child theme function changes to insert copyright in footer

Hello,

I set up a child theme incorporating TwentyEleven but now can’t seem to make any new changes. I want to create a footer with my copyright details so I made my own php file within my child theme and copied in the footer code from TwentyEleven, adapted with my copyright details, but it doesn’t work.

I managed to use the following code in style.css to remove the standard ‘Recent Posts’ and ‘Proudly powered by WordPress’:

.page-template-showcase-php section.recent-posts {
display: none;
}

#site-generator {
display:none;
}

I don’t think this is interfering with the child theme but thought it might be useful background.

Is there anyone who could help me with step-by-step instructions and code to properly use the php function in the child theme so that I can incorporate copyright details into the footer?

Many thanks,

Preeti