When you translate the structural component, you translate a word/phrase where it lives (as opposed to Translate Interface, where you get a huge list of the word appearing all over the site). 

You click on Structure, and you'll either go to Content types or Profile types.

As you can see, Content types are things like blogs, homework, and lesson records. For example, if you click "Blog entry", this doesn't mean you translate the actual content of a blog. By coming here, you're translating the structural component of all blogs (the parts that are always the same in each blog). 

Profile types are one of these:

• Location & language
• Profile
• Teacher Profile
• Staff Profile
• Course & tests
• Needs & company
• Contact details
• Company Profile
• Payment