There was a thread on this very recently. The point was made that everyone talks about TV, BBC, FIFA, EU, and dozens of others without turning a hair. When they first met these things they probably thought "What in heavens name is a TV? Why can't they just say television, it doesn't take much longer?" but they soon got used to it.
There are not many acronyms in frequent use on Gransnet - it is mostly the ones for words that are used all the time - H husband, S son, D daughter, GS grandson, BiL brother-in-law, often with a D in front of them to stand for dear (or dratted, depending on how the poster is feeling) and DD2 for "My darling second daughter" and so on.
They are not obligatory, you don't have to use them, you don't have read them. You do just as you want to, no-one will criticise you for it if you type out the whole lot every time, they will accept it. but after a couple of weeks of reading other posts, you will probably find that you have absorbed the ones you need and can ignore the others, or look them up in the glossary in the link up the page if you want to know what they mean.