The relative path should be relative to what directory you are in when you run the command. So, it all depends on where you are running the copy command from. For example, if you were in the "c:\new>" directory and wanted to copy logs in "c:\test\today\first\log" using a relative path you would type:
copy ..\test\today\first\log\*.log
What this command does is first go back one directory since you're in "new" and then from the root goes into test\today\first\log
Any time you want to move back use ..\ and if there are more than one directories you need to go back you would need to go back multiple times. For example, if you were in c:\test\today\first\log and wanted to copy to the new directory using a relative path you would type:
copy *.log ..\..\..\..\new
Of course it would be easier in this example to use a absolute path and type:
copy *.log c:\new
Hoep that helps, also you may want to read the below page if you haven't already.
https://www.computerhope.com/issues/ch001708.htm