It's easier to train a puppy or older dog if you have access to a park or garden. People who live in an apartment have a different problem.
The puppy basics are pre-programmed, the dog needs to relieve itself at regular times, such as:
-After eating
-After play or exercise
-After, or sometimes during, excitement, such as a greeting
-After waking up
The body language for all dogs is the same:
-Sniffing the floor
-Circling
-Running with his nose to the floor
-Getting ready to squat
When you spot the dog doing these activities, interrupt it and take it outside. Avoid picking him up if you can, you want the dog to learn to walk to the back door when it wants relief.
You need to have decided and selected a toilet area away from activity and distractions. Choose an area that's easy to clean and have clean up materials handy (plastic bags, pooper scoopers handy). You should aim to clean the waste immediately.
Using word cues
Select a phase that you would be happy saying when standing next to your mother, and use it every time the dog relieves itself. In time, the dog learns to associate that phase with the elimination. Keep it simple "Time to go" or "Pee Time" are simple enough, or you could simply whistle. Be consistent with the tone of the whistle though.