Okay, i dont want to be left behind but how do i figure this potty training out?

When i realise bub is trying to poo in his diaper, i bring the potty and he will come running and try to sit with his pants on. But if i dont do that, he wont tell me he wants to go. He only comes to me after.

If i put him on the potty he will pee in it and if he doesnt want to go, he will get off immediately.

What can i do to help him learn to communicate it to me before and not during or after?