Disability Tax Credit question

Hello,

I'm hoping for a bit of information in regards to the DTC as a person who is claiming someone as a dependant. I was told I have to send a letter with a wet (ink) signature and that I should include the SIN and DOB of the person who has the disability that I'm claiming.

What exactly should this letter look like? I was tols it should include what I do for them such as how I do their laundry make their meals pay the bills etc. But is there any particular format this should be in or do I just start writing?

Any help is appreciated!