Start by creating a circle using elliptical shape tool.
Using line tool create body of the stick man.
Using line tool create arms & legs of the stick man.
Create the rear arm and legs using a slightly different shade.
Since one pose is completed group the layers. Duplicate this group and hide the original one. In this group adjust the body parts as shown in the image below.
Similarly create more groups for each pose of walk cycle. Each image below belongs to one group of walk cycle pose.
We have created 7 different groups of poses. Good enough to create a nice walk cycle. Using custom shape tool create a tree shape. Place this layer behind the stick man layer groups.
Duplicate and place as shown in the image.
Merge the tree layers. Create 2 duplicates. Place one on each side of the original trees layers. Merge all tree layers.
Open animation window. For the first frame keep the position of tree layer as shown in the image.
Duplicate frame. Move the tree layer and move it towards left. Try to keep the appearance of tree layer as close as possible to the previous frame. This will ensure a smooth loopable animation.
Press the tween button in animation window. Apply settings as shown.
Delete the last frame. Now we have 7 frames and 7 poses groups.
Select each frame and keep hiding /unhiding walk cycle pose groups sequentially.
Press Ctrl+Alt+Shift+S to save an optimized animated GIF.