I was recently asked about embedding gadgets like the "Feed the Koi" so here is an overview:
First, click on the blue link amid the swimming fish to reach abowman at http://abowman.com/google-modules/fish/  and copy the string of code from where it says "embed."

Then  go to the Design tab at the top of your blog. Open it:

 

Click on the top link - "Add a Gadget" and the following box will appear:

Then choose one of the options (or better yet, investigate them all) I added the Koi at the "HTML/JavaScript" option.
 
 
  This is what you will be pasting in:

Finally, paste it into the large white area, and added a caption up at the top:  Save. Then "view blog" and see if it worked. If not, just try again. Getting there is more than half the fun! The first time this worked, I was plagued by delusions of grandeur.