You would enter any amounts that you earned in a foreign country before you came to Canada in the 'Residency Changes' section. Income that you earned from a foreign country after you came to Canada can go on the foreign slip.
You don't need to enter anything under "Enter the portion of foreign income exempt under a tax treaty"? or "Tax treaty exempt amount" unless you have income that is exempt under a tax treaty. If you are not sure if you have anything like that, then you'll need to look at the tax treaty between Canada and your country, or talk to someone who is knowledgeable in such matters.
