If you're lifting weights and exercising, you should be monitoring your protein intake pretty closely. Protein is the building block of muscle. When you exercise and lift weights, you are breaking down your muscles. The idea is to grow them back stronger than they were before you tore them up by lifting. If you're not getting enough protein, your muscle building stops, no matter how much exercising you do. Enough protein will help you rebuild faster and stronger, and you'll be ready for your next workout (wait at least 48 hours after working a muscle group before you have at it again.)
There's a lot of debate about how much protein you should be getting if you're trying to build muscle. One thing is pretty certain, and that is that if you're lifting weights, you should be getting AT LEAST 130 grams of protein a day. Some experts think you should get 1 gram of protein per pound of your body weight, others think as much as 1.5 grams per pound of your body weight. I'm 175 pounds, so if I wanted 1.5 grams per pound, I'd need 263 grams a day. That's double the minimum.
The beauty of protein is that it's effective for all body types. Even if your goal is to have a net loss of weight (gain more muscle and lose fat) you need to pack in the protein. THE MORE MUSCLE YOU BUILD, THE MORE CALORIES YOU BURN. And not just when you're working out. While you're sitting at your desk or watching TV, your muscles are eating up calories. This is why weight training is so good for weight loss, much more effective than, say, jogging in the morning. (Cardio has it's place, more on that some other day.) Another beautiful thing is that you can have a protein shake along with some fruit as a meal replacement, saving you lots of calories and filling you up so you don't feel the need to eat as much.
I've found that if I eat well throughout the day, I get around 150 grams of protein from food. To give a brief example, the day's meals would consist of things like a 3 egg cheese and ham omelet for breakfast, cottage cheese and fruit for a snack, a sandwich with meat or tuna at lunch, some almonds or peanut butter on celery for a snack, then chicken or another meat for dinner along with steamed veggies. (Everything according to serving size. So if I say peanut butter, for example, it's 2 Tbsp with 8 g protein.) I usually also throw in an orange and a banana in there somewhere. To bump my total up, I usually have a protein shake and/or a smoothie with protein powder added each day. A protein shake is best taken right after a workout, and can give you upwards of 50+ grams of protein. My "shake" is just powder in water or milk. Not the most delicious thing, but this isn't a treat, I'm in it for the protein. Use Whey protein as your powder; you'll get other proteins from your food. Whey is superior to other proteins as a muscle builder.
To sum up, get at least 130 grams a day, and depending on your weight, you should probably bump that total up to at least your body weight, and maybe even more if you want to see the benefits protein can give you. Get it in your diet--eggs, fish, meat, dairy, nuts, etc, and supplement with whey powder, along with muscle building exercises, and you'll lose fat and put on muscle.