That's kind of a tough question, but a couple random things that came to mind initially.
How old is your son? But the basic thing to keep in mind is, have fun, both of you!
Don't make it adversarial between the player and DM.
Start each game with presenting the plot hook(s) or some basic direction for opportunities (you can even have more than one plot hook that leads to the same adventure, just the player doesn't need to know that it would have been the same either way -- but at least having a choice is a good thing). Then the player generally decides to go off and explore/rescue/kill/etc based on the motivation and plot of the adventure.
he enters the first area, describe thge surroundings and then have him describe what he wants to do (investigate the statue that you mentioend in the description etc) and so on back and forth from room/location to next room/location. Then once combat starts, describe it thematically first (out of the corner of your eye you spot a group of jackle-like humanoids rushing towards you through the bushes) and then ask for initiative.
think of it as a story, there is some pacing involved and some general things in common such as the setup, the buildup, the climax, and the resolution.
try and mix up the types of adventures a little (don't have all underground in dungeons, have some outside in the forest of in an abandoned building, etc). if you're using prepublished adventures those tend to be action crunched and less story, so if both you and your son enjoy some story then use your creativity to add some (even something simple and just make up more as you go along -- you'll find a story can usually build itself based on the types of questions your son may ask of the NPCs etc depending on how inquisitive he gets).
A lot of how the game plays really depends on the style and preference of the DM and players. Some prefer less story more action and dice rolling, others like it the other way around, etc. Some prefer dungeon over wildrness settings, some prefer political and interactive roleplaying over combat where several sessions may go by without rolling a single attack roll.. some prfer low magic of high magic, etc. etc.
so getting a good idea of what type of style(s) you and your son like will make you both more 'in to ' the game and "how it plays out" really comes from whatever natural flow the two of you have -- as long as you're both having fun then you're playing it right!