The text in the image means,
For works published after 1989, a copyright notice is not required for a work to enjoy copyright protection. If you use an unmarked work in a way that violates copyright, you cannot defend your use by claiming that the unmarked work is not under copyright.
In most nations, all creative works are automatically under copyright per the Berne Convention. Prior to widespread adoption of the Berne Convention, authors needed to explicitly write a copyright notice on each work to make it covered under copyright.
A notable example of such a failure to mark a work is Night of the Living Dead published in 1968, which did not include correct copyright markings and became part of the public domain immediately. Such an event can no longer happen under modern copyright laws, since copyright now applies by default, not because of a marking.
The only effect copyright markings have in modern use is on innocent infringement. If you infringe a modern work the doesn't have copyright markings, you still infringe copyright, but you may be able to reduce the penalty by claiming that you didn't know copyright applied to the work. If the author includes a copyright notice, then you cannot claim ignorance of copyright.