
Welcome to the forum, I am sure you will find it full of useful advice as your pup grows up.
You just need to teach him the sit command and the stand command separately. When he comes to you and sits automatically say 'sit' as he does it and good boy, give him a treat. To put him into a sit from standing, take the treat to his nose, just out of reach and put it to the back of his head with the sit command, he should automatically sit. To teach him to stand, bend down next to him, sideways on and put a treat infront of his nose, say 'stand' and gently touch his stifle (the rounded bit on his back leg) and gently push it away from him into the stand. Praise and treat. For the down, take the treat to his nose again and bring it down between his front legs towards his chest.
Hope that is clear, most important thing is you only say the command once or he will start obeying it after 2 or 3 attempts which you want to avoid.
Good Luck with your new pup and make the training sessions fun.
Sandra