Do they plan on starting treatment right away or are they waiting until all genetic results are back first? Do you know what kind of genetic tests will be ordered? Some tests are a 'panel' that only look for a relatively small number of mutations (i.e. about 100), vs. the most thorough test (Ambry Amplified) that has identified, to date, over 1,500+ mutations. If at all possible, try to get him tested for all mutations, to be thorough.
When someone is diagnosed with CF, what comes next with treatment will depend at least in part on what kind of symptoms led to being initially tested. Is he having growth/weight gain issues, or trouble with digestion? Likely treatment in that case would be starting on pancreatic enzymes whenever he eats, to aid in the digestion of food (cf causes a condition caused 'pancreatic insufficiency' for most who have it, leading to problems w/ digestion.)
He will also start some type of airway clearance- how much will depend on his symptoms. Has he ever been diagnosed with asthma or other respiratory disease or have a history of frequent illness? His dr will likely put him on medication (inhalers or via nebulizer) that his dr deems appropriate based on his individual symptoms. They'll also take a sputum culture (mucus from his airways that they will have him spit up if possible, or swab from his throat) to see if he is growing any bacteria in his airways (common w/ cf) and probably take a chest x-ray. Treatment is very individualized with CF so they will learn as much as they can about your son and then decide based on this information how next to proceed.
I hope you get clear answers from the genetic testing and get started promptly with appropriate treatment!