I do not know how to write a good letter.

I need to write a hardship letter to get financial assistance from Catholic charities to help pay for my rent. Please help me write this letter. I do not know how to write a good letter. Here is my situation. Recently, I have hernia surgery on Dec 21, 17 and due to that I could not work. As such, I have no money to pay for my rent and other bills. I have four kids and I am relying on welfare. Please help me write good letter. Thanks a lot for your help! Please do not copy and paste from other internet source. I need your wisdom.