I would look into Puppy Socials. There are several in my area that are either free of charge or cost about $5 per visit. There is no training involved, but there is always a qualified trainer in attendance that could answer questions. Is there an SPCA or a Humane Society in your area? They are an excellent resource for information and sometimes offer Puppy Kindergarten at a very reasonable price.

Now on to the behavior - you have had him in your life a short time. He still doesn't know you very well. He has been taken from his mother and put in a situation that he doesn't understand. He's probably stressed - and when dogs are stressed they act out (people too ) Your act of staring him right in the eyes was interpreted by him as an aggressive act, so he did what any dog would do - he growled. It would be the same as a young child throwing a temper tantrum if they are stressed - or scared - or tired.

The mouthing or play biting is going to be something that is going to take a while to break. Puppies explore with their mouth - it is instinctive. If the "ouch" method is not working (it doesn't work on all dogs) - you might have to try a different approach. Not all training methods work for all dogs.

When I first got Leo at 8 months his playbiting was out of control. I tried the "ouch" method and all it did was put him into a FRAP (Frantic Random Activity Period) where he would run around the house at breakneck speeds, jump over the furniture and tug and pull at my clothes even more. What eventually worked for Leo was "time outs" – every time he started play biting, I would give him a time out in his crate. What also might work is a calm "no bite" and give him something else to chew on. Being calm in your correction might be the key.

This is not something that you are going to solve overnight - it took about 4 months to break Leo of the playbiting. You have to be patient. Puppies are awfully cute , but they sure are a lot of work.

I would suggest you do an internet search for Boxer - Puppy - Training. You will probably get some sites that have a great deal of experience with training that particular breed.

Good Luck