The barbell squat, deadlift and bench press are lovingly referred to as the "Big Three" exercises. When done correctly and together in a workout program, they hit oh-so many muscles in your body, teach you coordination and stability, and build incredible strength. If you're new to lifting, learning these exercises is a great place to start.
Image by greg westfall.
In reality, the squat, deadlift and bench press are all effectively full-body exercises. A squat, for example, initially looks like it only works out your lower body, but pretty much everything from your traps (upper shoulders) down to your heels are recruited for the movement. With just one "Big Three" movement, you engage and develop a ton of muscles that normally might require several movements. Overall, they're just a more efficient way to get stronger.
At the same time, some people don't have a healthy shoulder to safely bench, a healthy spine to deadlift without pain, or feel comfortable squatting to an appropriate depth. That's OK, there are other alternatives to these exercises that still help you get super fit and strong.
As a few examples, you can dumbbell press instead of bench, you can Goblet squat instead of barbell squat, and you can do cable pull-throughs instead of the deadlift. Keep your own abilities in mind and get stronger without hurting yourself.
If you're still learning, you obviously don't want to jump into heavy weights right out of the gate. They're fantastic exercises, but they're also very, very technical. Take the time to learn the ins and outs.