I went to put in reverse it made an awful noise

My blazer was driving fine last night and then this morning I went to leave for school and it started but when I went to put in reverse it made an awful noise and wouldn't go. So I then tried putting it into 1st and it wouldn't go into any gears but it only made the noise when I tried to put it in reverse. My dad said I need to adjust the clutch. Any ideas on how to do so? Oh and when I turned the truck off I could put it in 1st again.