Step 1: Get the extension.
Step 2: Go to any web page containing a recipe
Step 3: Look for the Yumprint button to slide in from the top right corner (this will only happen if a recipe is actually on the page)
Step 4: Click the button
Step 5: Press Save
Step 6: Choose a cookbook
Step 7: Repeat as many times as you'd like. There's no limit to the number or size of your cookbooks on Yumprint.
More detail about the Yumprint Extension is in this post.