Scratch

hello i need alittle help please
ok  how do i have a sprite when it start at the bottom of screen moving vertically i only move it horizotally so that it go up to hit another sprite? i dont want to hold it with arrow but just move it from side to side before it hit a sprite at the top of the screen? there will be another sprite moving up i dont want it to stick to. i want to use right left arrow to direct them in a position to hit a moving sprite going left to right  at the top of  screen. also when it hit sprite at top make a sound . when game over the screen say game over
thank you