Why do my stitches look like this?

Hi, my name is Ellie.  I recently bought my first sewing machine and was so excited to try it out!  I got the Singer Esteem II from Wal-Mart.  I did a few practice stitches on an old tshirt, but I think the stitching looks odd.  I apologise for my n00by terminology in advanced.

Here's what the top of the fabric looks like:


And here's the bottom:


Does the top of the fabric look wonky to you guys?  For the straight stitch, I was told that both sides of the fabric should look more or less like how the bottom side looks.  The top side shouldn't show the little "loops."  Also, the top side of the "thicker" zig-zag stitch just looks messy.

With this being my first sewing machine and all, I don't really know what to expect.  I've tried (aimlessly) fiddling around with the length, width, and tension.  Am I doing something wrong, or is it the sewing machine?

Thanks!

Do you have a ball point needle on the machine? Stitching on a t shirt which is a stretch material, you need to use a ball point needle.  Best to try to practice on a piece of cotton, and a universal needle, 80/10 size, work with your tensions, now that you have changed them, get the stitch corrected. T shirts have a stretch to it and possibly that is the problem.  Don't give up, if all else fails, take the machine back.

I agree with the poster above. Start with quilting weight cottons and not knits (like t-shirts). The bottom left pic of your 'top stitches' pics - it seems like the bottom tension is too loose. But, other than that the stitches don't actually look too bad! Stay away from the zigzag stitch that is like a double or triple stitch (the first pic), until you get a hang of the regular stitches. Just keep practicing!