As a beginner in the weight room, you need to keep it simple. There’s no sense in performing advanced exercises if you lack the strength to do the basics. Prepare yourself for more intense moves by first building up a strong core.
(Here’s a guide to assessing your core strength in 5 minutes.)
Contrary to popular belief, Sit-Ups and Crunches are not the solution to building core strength. Instead, you should start with exercises that engage your entire core and strengthen critical stabilizer muscles. These will increase your stability and balance, while helping you build a foundation for strength.
Below is a core workout especially for those who are just starting out. Perform these basic core exercises for beginners two to three times per week at the end of your training sessions.

Basic Core Exercises for Beginners

Supermans

Easy to learn and perform, Supermans strengthen the often-neglected lower back, a common source of pain. They also provide a great full-body stretch to finish up your workout.

• Lie with stomach on ground, arms extended overhead and legs straight
• Raise arms and legs as high as possible and hold for five to 10 seconds; keep arms straight and core tight
• Slowly lower and repeat for specified reps

Sets/Reps: 3-4×20

Bird Dogs

• Assume all-fours position with back flat; look straight ahead
• Slowly raise right arm and left leg and hold for five to 10 seconds; keep core right
• Slowly lower and perform on opposite site
• Repeat for specified reps

Sets/Reps: 3-4×20 each side

Planks

• Assume plank position with elbows under shoulders, back flat and eyes focused on ground
• Keep core tight and hold the position for specified time

Sets/Duration: 3-4×60-120 seconds

• READ MORE: 
  5 Painfully Common Core Workout Mistakes 
  Try the Pallof Press to Build an Iron Core
  The 27 Best Core Exercises for Athletes
  Photo:  reliefandwellness.com