It is very easy:
2. Click on "My groups" (under your profile, in the main page)
3. Make the groups that you want. For example "Primary 1", "Primary 2", "Primary 3"...
4. Enter the names of the students in each group, and a password for each one of them.
5. Whenever you find a good exercise in englishexercises.org, click on "Add this exercise to my students list", and choose the student(s) that you want.
6. Your students can log in with their name and the password that you gave them, and they will find a page like this:
There is no instructions to generate a new one...