What are the pro's and cons of pre work out supplements? How does it enhance performance while working out? Is there any side effects?

Most of them are simply stimulants.  Sometimes they're full of sugar, a bit of protein, and often creatine, and possibly nitric oxide (ala NO Explode).

Recently the stimulant is caffeine or B vitamins, in the past it could have been ephedrine, pseudoephedrine or some other pre-amphetamine or worse.

Looking at NO Explode, it has a bunch of stuff in it, Creatine, B-Vitamins (the preworkout might have caffeine also, based on the matrix on this page: BSN N.O.-Xplode at Bodybuilding.com), and nitric oxide.

Nitric oxide works as a vasodilator -- it opens up your blood vessels and allows more blood to flow. (It's also one of the active ingredients in viagra)
Usually you'll have more energy while on nitric oxide.

Side effects:
  • Blurred vision.
  • confusion.
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position.
  • sweating.
  • unusual tiredness or weakness.

Caffeine stimulates the Central nervous system allowing you to focus better. It also can raise your heart rate and blood pressure.

Side effects:
  • Caffeine is addictive and can have withdrawal symptoms including headaches and low energy
  • Caffeine is a diuretic, make sure to stay hydrated when using caffeine
  • Could keep you up all night.
Creatine is found in muscles of all animals. You can get it when you eat.  It helps provide a little extra push when you're working out. You might use it to get one or two extra reps or a few extra pounds when you first start using it. It also brings more water into your muscles helping you reach hypertrophy.

Side  effects:
  • Dehydration -- it draws water away from your body to your muscles, you'll gain weight, but it's water weight.
  • Is an allergen and can trigger asthma
  • There is some concern that it could harm the kidney, liver, or heart function. However, a connection between high doses and these negative effects has not been proven. Creatine can also cause stomach pain, nausea, diarrhea, and muscle cramping.
  • There is concern that combining Creatine with caffeine could lead to conditions causing a stroke
creatine: Uses, Side Effects, Interactions and Warnings
Caffeine vs Nitric Oxide - Which to rely on? This article indicates you can use both at the same time, but I don't think that's such a good idea since caffeine is a vasoconstrictor and NO is a vasodilator.

Each of these is safe enough on their own. When you mix it up in some unregulated pre-workout mix all bets are off.  I'd recommend trying one of the three in isolation from a trusted brand -- though I'd lean strongly to just getting a cup of coffee before hitting the gym in the morning -- rather than taking a crazy mix of stuff that you aren't sure what's in it.
I have a flat saggy bum and some belly fat. I have no muscle. How do I get a slim stomach and a bigger toned bum? Should I lose weight with a caloric deficit or gain muscle?

If you are a nooby, there is a golden exception to all this.Newbie-gains!So, use 3 weight-training sessions at which you should employ a circuit.Supplement that with 1–3 cardio sessions. Light intensity, 30–40 mins.Steer away from white sugar, fat+carb combinations (heavy ones, like, carbonara with it's sauce) and too heavy processed foods.The more processed the worst.Aim for high

What will motivate myself to work faster?

Different people are motivated by different things and the following may be useful starting point:Self-Improvement: How can I motivate myself to work hard? - 3600 answersHow do I stay motivated? – 1360How do I motivate myself to study? – 1200What are the best tricks to keep yourself motivated? – 1200

How to turn big fat belly into six-packs

First of all, no sweet, no spice, no butter type food, no fat, no salt and low carb high protein diet. No sweet means not even fructose. No fruit. Not even any fruit juice.Let's see if you have big belly then