With CPAP therapy in the treatment of sleep apnea, patients wear a mask over the nose (nasal mask) or a full face mask which covers the nose and the mouth. A full face mask is used when the patient is a mouth breather. Full face masks can be challenging due to their larger size which means a greater surface area and potential for mask leak. So sometimes a mouth breathing patient will prefer and choose to wear a smaller nasal mask WITH a chin strap to help keep the mouth closed.
A chin strap MIGHT keep the lower jaw pulled up, but it does not keep the lips together. So for some, a chin strap might work, but for many they do not. You would have to try one to see if it works for you.
Primary snoring is snoring without the presence of sleep apnea. While products are available for primary snorers, those with sleep apnea need oral appliance therapy or the gold standard which is CPAP. Remember that snoring is just one of the symptoms of sleep apnea, If you have sleep apnea and simply eliminate the snoring, it does not mean you are resolving your apnea.
Have you been diagnosed with sleep apnea?