Here's what your events could look like to have basic functionality. You click buttons to setup the list of commands and clicking run will make the cat move.
global number running=0
global number step=0
global text cmdList = ""
global text cmd = ""
clicked on LeftButton
---- add "left," to cmdList
clicked on RightButton
---- add "right," to cmdList
clicked on forwardButton
---- add "forward," to cmdList
clicked on clearButton
---- set cmdList to ""
clicked on runButton
---- set running to 1
---- set step to 0
compare: running = 1
every 0.5 second
---- set cmd to tokenat(cmdList, step, ",")
---- add 1 to step
---- compare: cmd = "forward"
---- ---- cat: move forward 32 pixels
---- compare: cmd = "left"
---- ---- cat: rotate 90 degrees clockwise
---- compare: cmd = "right"
---- ---- cat: rotate 90 degrees counter-clockwise
---- compare: cmd = ""
---- ---- set running to 0
From there the rest is just visual stuff.