CD-r are use once only. Once recorded on you cannot add more data
I don't think that is quite true - you can add data in small amounts until the disc is full or until you 'close' the disc ( the equivalent of locking it) to prevent the addition of more data. True, you can only record on them once, adding until they are full - like filling a filing cabinet until full. I burn files to CD as a back up, but not all at once. It is not possible to erase or write over the data once it is burned to this type of disc. You can reuse CD-RW type discs.
There are various options available depending upon the software that comes with the CD/DVD write drive. Nero, Easy CD, Sonic, Power2Go are some examples of software available. Any PC with a DVD writer installed on purchase will automatically come with CD/DVD burning/creating software. And of course, they all work slightly differently

so I wouldn't like to say definitively what you are able to do on your own PC.
What is "formatting"? Do you have to do that before you put the data on?
No, that should not be necessary.
Nell