Sometimes a dog dosnt know what you wan tfrom them when you take him outside to potty. Tell him to go potty (or whatever word you use) several times over and over. When he does go praise him like crazy and go immediatly back inside so he realizes that is why you went out in the first place and now he can go back inside. In the begining you have to set up times when you think they should go like when you first wake up take him outside and dont let him back in until he has gone, same in the evening before you go to bed. My girl was VERY stubborn, she did not want to be out in the cold so she would sit by the door wanting back in. I had to pretend to be doing something outside so she didnt think I was putting pressur eon her, she f thought "well as long as were out here I'll go I guess" and eventually she realized the sooner she goes, the sooner we can go back inside.
I also taught her the bell trick, hang a bell by the door that he exits out of and use his paw to ring the bell everytime before you go out. Pretty soon he'll get the idea!
Oh and he is just gorgeous!