You make variables for the screen coordinates and make a for/next or do/loop that slowly increase the variable in the direction you want the sprite to move.
` Make an image
ink rgb(0,255,0),0
box 0,0,50,50
get image 1,0,0,50,50,1
` Set the starting x and y of the sprite
x=0:y=200
` Set a timer
tim=timer()
do
` Show sprite
sprite 1,x,y,1
` Check if the timer is up
if timer()>tim+10
` Increase x coordinate by 5 pixels
inc x,5
` Reset timer
tim=timer()
` Check if the sprite is off the screen
` If it is reset x to zero
if x=>640 then x=0
endif
loop