Hello and welcome.
There's a whole world to see, but there are some things you can do to see it better.
If a place is well known or famous for some reason, there is always a good chance that another member has posted it before. There are two main ways to help you to see what others have placemarked and posted.
First, it is always a good idea to check the Google Earth Community Forum layer, which is where
previous placemarks are identified (it is updated every few months, so a placemark you post today will be in there soon). To activate the layer, just check the box.

The second is to use the
SEARCH page. This method will detect posts too new to to have been included in the layers.
To add new information about a feature which has already been placemarked, make a reply to the placemark and post already in place. You can access the original post by left-clicking on it and then left-clicking on the link.
If you discover that you have mistakenly added a duplicate placemark, It is good GEC etiquette to remove it by editing your post and choosing the "DELETE" option.