RAW alone is NOT a format file type, RAW is the name of multiple file types that have the raw information directly from the camera’s processor, no other compressions or changes have occured to the file as say a jpeg would inhibit.
Canon’s RAW format is CR2, while Nikon’s is NEF, both are easliy opened by any Adobe product, and can easily be opened by whatever software came with your camera (not sure if Canons come with software or not to tell the truth though), it is an XSi, an amateur camera so it should have some software of some type.
Otherwise look for a file converter or some other software that can work with CR2.
They aren’t a weird format, it is your computer i am assuming you just don’t have software that supports the raw format, all you have to do is either make your camera save in jpeg, or do otherwise.
Just know this: RAW is the best stage any photo comes in, anything besides that isn’t original and only loses information throughout its lifetime in any other form.