What does plank do to your body, how to do it properly?

A simple exercise that is good for core strength, posture, balance, stability, endurance, and injury prevention, planks are workouts that can ensure you have a solid core. Its basic, dynamic, side, rotational and advanced forms have many variations. However, the standard forearm plank, where you rest your forearms on the floor, holding your body straight and engaging your shoulder, core and glutes, is the most common. According to Harvard Health, anywhere from 10 to 30 seconds is a good plank time. Those holding it should try to hold multiple sets with the right posture rather than have one prolonged set with poor posture towards the end. There is no harm in performing planks every day, on alternate days or regularly during workday breaks. Here's how to do a plank correctly and most effectively:

1) Lie on the floor, mat, or towel facedown. Ensure it isn't slippery and there is enough friction to get balance but not too much to hurt your arms and legs. 
2) Place your forearms on the floor, your legs extended, and your feet together.
3) Raise your body to form a straight line from your head and neck to your feet.
4) Make sure your hips aren't rising or saving.
5) Take normal, even breaths.
6) Keep your gaze down and ensure your abdominal muscles are engaged.
7) Once you complete 30 seconds, lower your body
8) After resting for 30 seconds, go for the next set. Do two or three sets, depending on your comfort. 

If this is tough for you...
Beginners can start with knee or modified planks, which do not put extreme strain but help build strength and recover from injury. For those for whom resting forearms down isn't comfortable, you can try the push-up position variation, where the hands are fully extended. Once you are comfortable with a knee plank, you can progress into forearm planks, full planks, side planks, planks with shoulder taps, plank up-downs, spiderman planks, plank jacks, one-leg or one-arm planks and more.