Each teacher takes individual responsibility for linking themselves with their classes. To link yourself to a class:

 

Go to Manage => Manage students / classes

 

 

Find the class you want to link to (e.g. 7y/Ma3) and click the person icon on the left-hand side.  

 

You will now be linked to that class in HegartyMaths. You will also be prompted to link to classes when you first start exploring the site: