forward number
fd number

This command makes the turtle move in the direction it is facing. If the pen is down, the turtle leaves a trace. Often used with pu (pen up), pd (pen down), pe(pen erase), back (bk) and wait.

(given that you have a turtle on the page)

pd (put the turtle's pen down)
forward 100
repeat 4 [forward 100 right 90]
repeat 36 [forward 100 back 80 right 10]