The Walking Lunge is a great exercise to build quad and glute strength, but it also works your core.
Don’t let your back slump. It will naturally tilt forward a bit, but try to keep a straight line from your back knee through your hips and up to your shoulders. Doing so will work your core.
Start from a standing position (you can hold weights in your hands for more resistance), squeezing your glutes and abdominals.
Lunge forward. When doing so I like to keep most of my weight on the heel of my forward foot. This helps me to keep my forward need from going past my toe.
Your knees should be bent at approximately 90 degrees.
Then power back up to a standing position, pressing through the heel of your forward foot.