After finishing the first copy, click "back" and then "go" again to make a second copy. But this is usually a waste of time, because CloneDVD will transcode again. It is better to split the "file creation" and "Disc creation" into two seperate tasks.
First, write into "files". You can check the files with any player software before burning.
Second, use the third button "write existing data" to write a it to DVD. The directory of the last file creation will be automatically pre-selected.
Then you can use the third button "write existing data" again to write additional copies.