I don't really recommend teaching your parents how to use a cell phone if they have a keypad phone, after all, it's very difficult to teach your parents how to type on a keypad phone, it's almost hard to teach them.
Like my mother is the kind of keypad phone, I used to teach her to use pinyin to type the name of the number, but how to teach my mother, my mother can not, and then if I want to save the number of the time, I help her to save, and never taught her to use pinyin to type again.
But if you have a smartphone, you can teach it. My dad uses a smartphone, and the best way to teach a parent how to use a cell phone is to give it to him and let him figure it out on his own. After all, figuring it out yourself is far quicker to remember than being taught.
But it's not all about letting them figure it out, you can teach them the basics and set up some infrastructure before they figure it out.
The basic operations that you can teach them are how to answer the phone, how to use WeChat and these communication apps, how to send WeChat messages and make WeChat calls.
Additionally like those typing it is best not to let your parents use the keyboard to type, it is hard for them to learn, so you have to change the keyboard in their phone to handwriting and let them write, it is much easier.