Your core is basically all the muscles in your torso that keep your body stabilized and balanced. Your core muscles start at your hip and make up your entire torso up to and including your neck.
Building your core is important. Your core helps you keep your balance, your posture is better, and with a strong core you can be and feel healthier. Strengthening your core can help reduce the likely hood of injury.
Exercises that build your core
There are many exercises that can build and strengthen your core. One of which is the plank. The plank is where you lie flat of the floor and push up till you arms are straight and you hold the position. The plank really works your entire core.
From the plank, turn your body so that you are reaching up to the ceiling with one arm. Your legs and other arm support your body.
A popular and effective exercise is crunches/sit-ups. While on the floor, place your hands behind and over your head. Then while doing the sit up, allow your arms to swing to build momentum. To make it more challenging you can have weights in your hands to make the movement more difficult.
Another good exercise is the hollow rock/superman. While on your back you lie of the floor keeping your abs tight. You then raise you arms and legs off the floor and hold the position for 10-20 seconds. Now roll over, with your legs and arms off the ground you should be positioned like your superman flying. Neither your chest or thighs should be touching the floor. After holding the position you roll to your back and repeat.
You can perform sit-ups and hip and back extensions on machines such as the glute hamstring developer machine if you have access to machines. When using machines and weights is is important that you use proper form; or you could potentially injure yourself. So it would be beneficial to get an instructor to show you how to properly use weights and machines.
Adding core strengthening exercises to your workout at least twice a week, will give you a stronger and healthier core. A stronger core makes your other exercise routines easier.