My partner told me that squats are a basic exercise, that it helps to improve the lungs so you should do squats daily to lift huge weights. Is this true? Are squat exercises helpful to reduce our body weight and belly?
Yes! Squatting -- as part of a proper regimen of exercise, eating and rest -- can lead you to lift huge weights, improve lung capacity, or reduce body weight. The squat exercises the body's largest muscles and is one of the most basic functional movements. Until the invention of sitting toilets, squatting was a daily necessity for all humans even into old age.
The benefits you get will depend on how you squat. To name just a few variations, you can squat with a heavy barbell on your back, with a dumbbell held in front of you, or with just body weight; you can do a few reps slowly or many reps quickly.
Looking at the letter of the question, no, you could do deadlifts instead. But in the spirit of the question, yes, you really should do a compound lift involving your legs and back. Try to pick at least one that you can do safely and without pain (front squat, back squat, ball squat, hack squat, standard deadlift, sumo deadlift). If absolutely none of them work and you've researched how to do them properly (Starting Strength by Mark Rippetoe and The Insider's Tell-All Handbook on Weight-Training Technique by Stuart McRobert are both good books to look into) then you could do leg presses instead - it's generally accepted that free weights are more productive than machines, but if you get injured doing free weights but not the machines, then in that unfortunate instance, machines are better.
Interestingly, nobody can really agree whether the squat or deadlift is better, even Rippetoe who starts off saying the squat's the best exercise period has a diagram in the back of his book that seems to suggest the deadlift is better. That got a chuckle out of me. I happen to prefer the deadlift because I can perform it more comfortably, also just conceptually because training to lift something heavy off the ground is an incredibly practical movement to train.
As for reducing the belly, I'm a skinny guy but was getting a bit self conscious about my belly sticking out, purely doing deadlifts, overhead presses and pulldowns I got it pulled in a bit. I couldn't really pinpoint which of the exercises was responsible, although I'd be inclined to attribute it to all of them due to the need to stabilise with my core muscles while performing those exercises. I don't have experience myself with fat burning, but I've read from numerous sources (which could be just a bunch of people referring to a single study, I'm not claiming that there's scientific consensus here) that beginners doing weight training see both fat loss and muscle gain.
"There are few things graven in stone, except that you have to squat or you're a pussy." -Mark Rippetoe So according to Coach Rip, yes you should be squatting. Squats are great for the legs, back, abdominal muscles, etc.
As for reducing your body weight and belly that is far more dependent on what you are eating rather than squatting.
There are three basic strength building exercises: squats, deadlifts and bench pressing. Direct to your question: do they help the lungs and should they be done everyday? Any exercise helps lung capacity, it's a common fact that only 31% of Americans get proper exercise, which is considered 2 to 3 hours a week...
So, everyday? with heavy weights? No, you need to set goals and based on those goals develop a workout program that you will follow for a long time (with on-going planned stages of change). Lifting HEAVY everyday a specific body part will lead to injury and boredom and result in leaving you worse off than not doing it.
My recommendation: set your goals (based on what you want and including nutrition), develop a plan (get help if you need developing a good plan) and just do it.