Can anyone explain how john connor sends his own father back in time in the terminator movie?

No. No one can explain that. Oh sure you can talk about changing the catalyst of the event (his father tells john it was he who sent him, but it was a lie, created by some historian who would like to create a time loop just to mess with the time/space continuum), but that will never explain the one unforgivable bone-headed explaination, especially since his father doesn't know he's his father and how can you be fathered by someone younger than you? Do dog years enter into this somewhere? No, No, just forget this question, wipe it from your brain, if you can do that you can enjoy the movie over and over again. But if you dwell on it your head will explode. I've forgotten about this question for over 20 years, and now it's back again AAARGH.