"Manitoba Education Property tax credit advance received" refers to any amount already deducted from your property tax statement or received by you after you applied for it. So you don't need to calculate it, you just need to check your property tax statement or any notice sent if you received an amount separately.
On the page after the one that asks about "Manitoba Education Property tax credit advance received", it will ask you about rent and months lived in. Fill in anything that applies to you. The third page asks if you shared the accommodation, but that only applies to people other than a spouse or dependent children.
One you've finished those three sections, you've finished with the Manitoba Education Property tax credit application. When you get to the Provincial Tax Summary, you should see the credit applied there.