With the bar in the crooks of your elbows, this squat variation can be challenging, but it also has many unique benefits. It's very effective at building the anterior core and the upper back, along with providing an isometric action for the biceps.
Set the bar in the rack at about hip level to lift it off. Step back and squat. You may notice that you'll be more comfortable going deeper with the Zercher. The box squat also works well with the Zercher position.