To add a visitor counter, you need to sign up to a site such as statcounter.com, which provides free visitor counters for websites. Once you have a counter, you can see how many people are visiting your blog and where they are from. To get started, just go to http://www.statcounter.com/ and click on "Register Now - It's Free (We promise!)". Follow the instructions to complete registration. Make sure you tick the box that makes your stats public, so everyone can see who is looking at your blog!
At the end of the registration process, statcounter will say 'here is your code'. You now have to add that code to your blog. Select and copy the entire code for the 'Visible Counter' so that you are ready for the next step.
To add the counter to your blog, you need to go to your dashboard, then click on 'Layout', then 'Add Page Element' in the place where you want your counter to appear. Find the element called 'HTML/Java script' and click 'Add to Blog'. Add a title if you want, and then paste the code from statcounter into the box, and click 'Save Changes'.
Your counter should now be visible when you view your blog!
If you have any problems, ask your teacher!