There are two types od CDs
.. CD-RW which is a RE-Writable media. With this type of disk, YES you can delete and add files. This is very simular to a HDD, just using optical media instead of magnetic media to record to.
.. CD-R is "WRITE ONCE, Read many Times. Once a file has been written to the disk it is THERE permanately and can NOT be over written. With CD-R you normally "Close the disk out" when you have finished recording to it. Once it has been closed out NO Changes can be made. HOWEVER, if you have written say a bunch of files and have NOT closed the disk out, You can "mark" the file for deletion. THIS DOES NOT delete the file As it can NOT over write it. When the Disk is closed out, this file is marked as deleted in the File allocation table. SO Correct answer is YES and NO
quote ... 3. Packet Writing – used to record data to a CD-R in "packets", allowing extra information to be appended to a disc at a later time, or for information on the disc to be made "invisible". In this way, CD-R can emulate CD-RW; however, each time information on the disc is altered, more data has to be written to the disc. There can be compatibility issues with this format and some CD drives. End quote.
NOTE the "invisible" = Deleted, BUT still there and can be recovered. This is somewhate simular to deleting a file on a HDD. The file is ONLY marked as deleted and is STILL There UNTILL the sector is over written - With CD-R you CAN NOT overwrite.
Side comment, Yes it would have been easier to just google "CD-R" and select wikipedia and read.