This is for joining the work. What some knitters like to do is to cast on an extra stitch. They will slip this stitch from the right hand needle with the working yarn to the left needle and knit these two stitches together. This closes up that gap. I like to knit the first stitch with the working yarn and the tail. On the second round, I knit these two stitches together and pull the tail tight. You have to be careful with this so you don't twist the work. At the beginning of each needle, slide the first stitch as close to the tip of the needle as you can without its falling off. Knit that first stitch or two by pulling the yarn as tightly as you can. Then you can relax and knit the rest of the row. Repeat for each needle. I've noticed that this is particularly important for the first few rows. This is when you will get these ladders. If you get ladders the first few rows, it's almost impossible to correct it later on in your work. If you absolutely can't get it, try Magic Loop on circulars. This is what I use all the time. Again, with Magic Loop you have to be careful with the ladders at the start of each needle.