I will try and simplify it for you! The code is actually created from going to http://www.meebome.com. It has a 3 step process to create your sidebar widget and setup an account with them! After the 3rd step, it has a box to copy the code you need to put into your sidebar widget!
As the process says, log into your WP admin => Presentation => Sidebar widgets. There you have to drag the Meebo Widget from the bottom into your sidebar. Once it is in the sidebar list, in the top right hand corner of that widget is an edit button. That brings up the editor for that widget where you will need to copy the code that you got from Step 3 at meebome.com! Then just save the widget and save the changes that you made to the sidebar widgets!
That should place the meebome widget on your site! Now, all you have to do is go to http://www.meebo.com and login using the username and password that you created in Step 1,2,3 from the meebome.com site and it will bring up a web based IM! When logged in there, it also has your site IM widget so if a user replies on your site, you are alerted! It works great!
Hope that clarifies this a bit for you! Seems a bit duanting, but just go through it step by step and it will all make sense!