I tried to find this as I think it's a common issue but could not in the search.
I own a .com domain which is my main site but I also own other tlds for the same domain name such as .net, .mobi, .org, etc.
Is there something I should be doing to configure them somehow to be apart of my main .com site or should I just sit on them?
.com, you can serve different content through them or you can just park them and not make them resolve. This all depends on many other points you did not describe. – Patrick Mevzek May 13 '18 at 18:49