Sorting posts by meta key and value

Hello,

My idea is to sort posts by their average rating. Currently I’m using a plugin saving the averate rating for each post for me in a meta key called crfp-average-rating.

Now I want to sort my posts based on their average rating (highest first). I’ve look around and found multiple threads describing small parts of the process. But I don’t fully understand where to put what.

I assume I have to first create a function which I then can use in the loop? At least that’s what I’m understanding from these links:
http://codex.wordpress.org/Displaying_Posts_Using_a_Custom_Select_Query
http://wordpress.org/support/topic/how-to-run-a-wp_query-on-both-wp_posts-and-wp_postmeta-simultaneously?replies=7
http://kovshenin.com/2009/customize-posts-order-in-wordpress-via-custom-fields/

If anyone got any idea how to make this happen I’d surely appreciate your help!