To use walk_designer script you will need your figure to walk in straight line first.

You can make it manually by offsetting each hip and feet zTran parameter but it will last forever so below you can download another script that will make it for you.

Just select your figure (with walk cycle applied), set the wanted number of frames for the animation and run the script (make sure that figure has IK switched on on feet and/or hands).

You'll see the window:

start: - frame from which cycle starts
end: - frame where it ends
swap: 0 or 1
offset: 0 or 1

swap - this is very useful - you don't need to make full cycle - make only half and set it to 1.
Then the mirrors will be done automaticaly up to last avaible frame.

ie if full cycle has 33 frames (fr.1 = fr.33) then the mid point will be at fr.17 (33 frames but only 32 unique, 32/2 = 16, 16 + 1 = 17 --- frame 17 is the first frame of mirrored part). So cut your animated cycle to 17 frames (using the frame indicator box) and then extend to ie 300 - that gives you only 17 frames with data and the rest is clear.

offset: type 1 here so it will automaticly shift your figure in required direction at the end of each cycle (or half of the cycle)

additional info:
If you want to use full cycle then in mirror type 0 (because no swapping is required) and 1 in offset.

if you only want to swap your cycle then type 1 in swap and 0 in offset ( but in thiscase you have to add one line in the script to erese the old data before applying new one).

Important.
1st rame (start) and last frame (end) MUST be exact mirror of each other for the actors with IK switched on and for the hip (only when using half of the cycle) and this can seem really tricky at the beginning.
Script MUST know which are required direction so there is a line inside the script where you can type it in - easy to find.

That script i did for myself so please keep it in mind when you will get mad at it:)
More: the code inside is very unprofesional - sorry.

BUT that script is VERY usefull when mirroring animation - every change you make to your 1st half of cycle then it can be applied to the rest of it in fraction of second - so you can check the result almost immediately.

Finally:
as you can see that walk designer script requires some work before it can be used so if you are still intrested just answer here and I will continue.

And maybe someone can make that script (cycle_animation)  more user friendly so others can use it without troubles.