Your camera is an APS-C 'crop' sensor camera. However, this is not about the overall dimensions of the sensor, it is about the format that you want to shoot in. The traditional proportions for film and a sensor are 3:2, which uses the full area of the sensor. However, many people post their images on screens that display in 19x10, or for image composition purposes even on 1:1. When you went to the screen to change the lines you would have seen a list of different proportions listed, as per the image on Newton's last post. In that case the camera reduces what the sensor records to the various proportions shown. The lines on the screen are to help you compose your image to the new proportions. On mirrorless cameras, which don't use an optical viewfinder, the image is displayed in the chosen proportion to the electronic viewfinder.
I would recommend, if you have not done so, downloading a copy of your manual from Canon, and use that to check these things - you will find it a wealth of information.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
