Its really simple. Just paste the rapidshare file download link in the address bar and go to that link. The page will show two buttons, "Premium User" & "Free User". Click the "Free User" button. It'll now ask to wait for 40-70 secs. After that a "Download" button will appear, click it and your download will start.
Similar to above, paste the link in the address bar and go to the link. At the right-corner of the page, you'll see 4-letters. Enter those letters exactly in the box beside the image and press enter. The new page will show a timer which will wait for 45 secs. After that a "Regular Download" button will appear. Click it and start downloading.