Sure Canada eta is not a visa, but its allowing you as an EU citizen to travel to Canada by air. Normally, its valid for 5 years, but at the point of entry the office will decide if you must allowing to enter or not.
And you have right to stay not more than six months though you have five years. If you want to staying more than six months, you can extend but it depends upon your circumstances.
Eta is not a working permit nor students visa, so if you want to work you can applying for work permit and if you want to study more than six months, you can applying for study permit, but programmes less than six months you do not need study permit.