The T6i is capable of two file formats for photos, JPG and CR2. The output file format can be changed in the camera menu system.
If you purchased a used camera, then it is strongly recommended that you reset the camera back to factory defaults. Most dealers perform this reset for you. Many private owners do not.
Set the top dial to “P”. Go through each menu item that you can find and perform a RESET if that option is available. You should find several places in the menus, including Custom Controls and Communications.
In addition to resetting your camera back to its factory defaults, as Waddizzle suggested, I'd strongly urge you to download a copy of the T6i user manual. In there, you will find instructions on how to select either RAW (your CR2 images) or JPG's as your Image Quality.
(This will probably be in your menu system by pressing your Menu button and choosing the first Tab - it will be in red and the sub-menu will be labeled Image Quality).
PS: Regular Image viewing/editing programs do not handle RAW files . You have to use specialized programs like DPP4, as Peter suggested.
12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.