Here are two pictures of something, I don’t know what happened.
I am knitting only, not purling.
It’s different than a dropped stitch because there isn’t a hole.
Thanks!
cj
You forgot to knit a stitch (maybe 2) and the yarn carried behind it. Look at the stitch under the loose thread and you’ll see it isn’t the same as the one next to it… Go to Fixing mistakes in the Tips videos and look at the one for “Correcting a stitch [I]without[/I] unraveling rows”.
I think you slipped the stitch to the right hand needle without knitting it, and it got carried across the work there.
Garter is the easiest stitch to knit but it is not the easiest to fix. You can fix it without ripping everything out to that point and doing it over, but it’s a little trickier than fixing stockinette. You can do it though.
If you do it all from one side you have to use the crochet hook to knit one and then purl one, in that sequence until you get it back up with the others. But you have to watch carefully that you get started on the correct stitch in the sequence. If you get up to the needle and it isn’t the right stitch take it out and do it over starting with what you didn’t start with the first time. 
Another thing you can do is to pull a knit stitch through with the crochet hook, then flip the piece over and pull the next stitch through as a knit stitch, flip again and repeat. That way you can do them all as knits, but again, you have to get off on the right foot, or they will all be wrong when you get to the needle.
I’m sure there is a video about fixing a dropped stitch, it would apply here, even though it is not a dropped stitch. I just thought those tips might help. Good luck.
There’s a vid about correcting a mistake without taking out your work.