Walkcycle is basic of animation like bounce ball, but it's little more complicated. I think animator must know how to make it. It's is simple but complicated. This material available in each animation lesson, wether 2D or 3D. If you want to learn this step on 3D software like Blender, you must have a rigged character with constraint or just armature with the constraint.
Constraint will be help us to animate the character, because not all bone in character must be driven by animator. Animator just need to drive the controller and another bone will be influenced by the controller. It's will be helpfull :)
For Blender user, you can download character pack by vmcomix on blendswap. The character is simple and have been rig by author. So you just need to driven the controller. The controller was replaced by custom shape rig.
On first frame, place the left foot controller in front, and the right foot controller behind. The hand must set too. When the left foot in front, the left hand behind. If you confuse, the character will be look like this. To grab the controller and move it, you just need to press with G on keyboard.
|pose on first frame|
Don't forget to insert keyframe with press I and select LocRot for insert keyframe into Location and Rotation of controller. Insert keyframe on all controllers that will be driven. Select the controller and copy the controller has been given keyframe with Ctrl C or press copy button on Tools (T).
|copy the keyframe pose|
Go to frame 10 and paste the stored pose filpped on to current pose with Ctrl Shift V or paste button with the Flipped on X-Axis active. Don't forget to insert LocRot keyframe with click I and select LocRot.
|paste pose with flipped feature|
To test animate, set the end first, because the default is 250 and we just driven untill frame 10. If you still make the end 250, will be wasting time from frame 11 - 250 before back to first frame. You can see the walk cycle, but the foot stay on floor and when the player back to first frame, you can see the movement not perfect, we just need some trick to fix that.
For fix the foot, you just need to go frame 5 and select the controller of forward foot. Grab it on Z-Axis like picture bellow and don't forget to insert LocRot keyframe with press I on keyboard.
|adding new keyframe on frame 5|
The walkcycle has not been completed. There is one trick to finish it pretty and you can repeat it again and again on animation or game. Switch the window into animation mode, so you can see the Dopesheet and Graph Editor. Keep focus on dopesheet, you will see the keyframe of controlles.
|keyframe on dopesheet|
|Duplicated the keyframe|
The basic of walkcycle almost done, you just need adding one keyframe on frame 15. It's the flipped of frame 5. You can copy the frame 5 keyframe and paste with flipped on frame 15. So, the dopesheet look like this.
If you want the character move forward, you just need to move the root shape. Be creative with your walk, so the character have a walk style. Good luck ;)