importing salesforce data using custom link

While importing the data from salesforce report, there is a point where power bi gives 2 options.

 . Production

 . Custom

I know how production thing work but I have no idea how this 'Custom' thing works. I tried searching on the net, in the documentations etc but could not get it.

It would be really helpful, if I could get a like which explains importing salesforce data using costum url.