A lovely initiative but not for the inexperienced dog owner.
We'd like to save all unwanted dogs.
It can be very rewarding but very challenging at the same time.
Many shelter dogs have no past history/ background forms given to shelter when they get surrendered by previous owners.
Ideally consider adopting a dog that has been temperament tested at the shelter so you know if dog is ok with people, children, if suffers from separation anxiety, barking or destructive behaviour, if it's reactive to other dogs and/ or other small pet animals and main areas of concern.
Shelter/ rescue dogs do need training and not all do well in a dog training school or dog training classes. And this is not a fault of the trainer neither of the owner nor the dog. Some have never been around other dogs before and the fact that been put around many dogs can be quite overwhelming for them.
Consider having 2 to 3 private training sessions with a positive dog trainer so she/ he can better access the dog. The dog may be able to join a small group class at a later stage or to continue with private training if it best suit him/ she. Don't rush.
A rescue dog needs time to 'gel' into its new home, to know that that new place is their 'real' home now.