These are for the mechanism for going from a machine name to a Fully Qualified Domain Name.
DNS searches can only look at a Fully Qualified Domain Name, such as mymachine.example.com. But, it’s a pain to type out mymachine.example.com, you want to be able to just type mymachine.
Using Search Domains is the mechanism to do this. If you type a name that does not end with a period, it knows it needs to add the search domains for the lookup. So, lets say your Search Domains list was: example.org, example.com
would try first mymachine.example.org, not find it, then try mymachine.example.com, found it, now done.
would try mymachine.example.com.example.org (remember, it doesn’t end with a period, still adds domains), fail, then mymachine.example.com.example.com, not find it, fall back to mymachine.example.com, found it, now done
mymachine.example.com. Ends with a period, no searching, just do mymachine.example.com
If you have your own DNS domain such as example.com, put it there. If not, ignore it. It really is more corporate than a home setting.