Step-by-step explanation:
Hi! So, to start off when I talk about a friend and use their name in the sentence, I capitalize the first letter of their name. For example in the sentence, I went to the park with my friend Adrianna, I capitalize the A in Adrianna because it's a person's name. This also works with family titles. This is because that title (Mom/Grandpa), is being used as that person's name. It's basically a replacement for the person's actual name. If my mom's name was Jane, instead of saying Jane went to the store, which could be talking about anyone and not specifically my mom Jane, I would say Mom went to the store. That way, the reader or the listener understands that it is my mom and that is what I call her going to the store.
Now, in the second part of this, it's basically saying that if the person is not using the title (Mom/Grandpa) as the replacement to that person's name, then you shouldn't capitalize the first letter of the title. For example in the explanation above, I said My mom's name is Jane, the reason I didn't capitalize mom here is that I'm not using it like a name. If I was to capitalize it in this sentence it would be like saying Jane's name is Jane, because I would be using mom as a name.
Hope this Helps! :)
Have any questions? Ask below in the comments and I will try my best to answer.
-SGO