To train a puppy, you need to make sure you take them out first thing in the morning, whenever they wake up from a nap, after each meal and before bedtime when they should be crated. When you take them outside, place them in the grass where you want them to go and say "Do your jobs." When they start going pee or poop, praise them over the top, "GOOD BOY/GIRL!". You don't have to make the association with the backdoor. They figure that one out all on their own.
In case of an accident, tell them "NO!", pick them up and put them outside immediately. Bring the puppy over to where you are cleaning and clean the spot with vinegar. Let the puppy smell the vinegar...Don't worry, vinegar dissipates in about 30 minutes. This discourages repeat offenses.
I highly suggest you crate train. Crating give the pup a sense of its own room and space. The crate should be just big enough for the dog to move around in. If you give them a bigger space, they will pee in their crate.
GL!