Cardio is strength/health of your cardiovascular system. When you do any exercise, it also exercises your cardio system. "Cardio" exercise - jogging, yoga, etc. - is low-intensity aerobic exercise - more low weights and high reps. It does not stop you from building muscle, but cardio exercise tends to build lean muscle (think of a runner or gymnast) rather than bulky muscle (think body builder.) Cardio is good for you, period, but if you want muscle size then you'd be more interested in high weights/low reps exercise.
Your weight IS affected by your muscle mass, and you fat content. But it's hard to tell which is which just by looking at a scale. That's why you can do a body composition test. To gauge your body changes, you'd be better off taking pictures of yourself, once a week or so. You can compare the pictures to see the changes.
You cannot measure the weight of your muscles. You can however gauge if you have gained muscle by the way your muscles have bulged. The "cardio" exercises on the other hand can compromise your muscle gain depending on how much you use it. Doing the "cardio" too frequently, too intensely, or for too long can definitely prevent you from gaining muscle.
Cardio doesn't change muscle mass at all. Cardio is healthy for the heart and will help trim body fat and if anything help tone and define muscles. As long as you get down to your 10% body fat range then gaining muscle mass won't be problem
It usually takes 3 weeks to see a change in your own body, 6 weeks for your family, 9 for close friends, and 12 for people you don't really know. Cardio is good for your heart and it also helps burn fat and tone muscles. If you want to build muscle you need to focus on weight and strength training.