Zenkutsu-dachi (Front-stance): If you go from a natural position (feet resting one shoulder width apart, both feet pointing forward) and take your left foot forward to roughly two shoulder width apart, your feet should be at the correct position for front stance. From here, bend this front leg, so if you had a tape measure you could have a straight line from your knee to your foot. Then straighten your rear leg. Your weight should be roughly 60:40 with 60% on the front leg. Your back should be straight and your buttocks should not stick out like a duck. This is a very basic description of a typical front stance. These measurements will not always work, these are simply just very general rules.
 

Zenkutsu-dachi movement: During a step forward, your rear leg does not just move forward, but instead follows a zigzag path along the floor. There are several reasons for this, which will become clear when you train in your dojo.

Begin one zenkutsu-dachi, which is one shoulder width apart. Then push or pull the rear leg inward to meet the front leg. Then Push off what was your front leg to take the other foot forward. Therefore your foot moves inward then outward.

Always be sure to keep your back straight, and not to bend or lean.