Getting used to unpicking stitches is something that only comes with practice. I recommend knitting a small square, then practice unpicking it. Start with stocking stitch then try other stitch patterns.
In the video below I show you how to unpick a row of stocking stitch stitch by stitch and then I show you how to unpick several rows quickly. I'll also show you how to unpick a row of lace knitting, including decreases and how to unpick several rows quickly.
The easiest way to unpick is to put a lifeline in and rip back to the lifeline but sometimes we don't think we need a lifeline or we forget to put one in. If you've not heard of lines, take a look at my tutorial.
Please ask any questions you have in the comments below. You can see all the previous Monday Mini Tips and other tutorials on my Tutorials page.