Good question - and there's a tutorial with pictures to help you. I think your problem is probably with the 1/4" seams. It's very easy for them to be off slightly, which makes everything else go wrong.
Go to the Main page, Click on tutorials. Click on the NEXT page. The tute you want is 'Beginner's Blocks #1 - the 9-Patch and Variants.' Scroll down until you find the part where she describes how to check to see if you're sewing a PERFECT 1/4".
Good luck!