Student accounts use Gmail to authenticate into Canvas (This is for Student accounts only not LC or Observer accounts). This means you must log into your School Gmail account first. This will avoid the 403 Error that can happen when you are logged into multiple Gmail accounts at the same time.
1) Go to https://gmail.com and enter your whole school issued gmail address (email@example.com) and click on the 'Next' button.
2) Enter your school email password and click on the 'Next' Button
3) Once you are in your School Gmail account, you will want to click on the Google Waffle icon which is in the upper right corner:
4) That will open a drop down menu with many icons in it. You are looking for the Canvas Icon (2) which is all the way at the bottom of the menu. You will need to click on 'More" at the bottom of the screen and use the slider (1) to move to the bottom of the menu. The icon really is there. Google won't let me place it any higher in the menu. That will take you and log you into Canvas automatically.