...but sometimes you will be directed to work into the front or the back loops only. It is important to follow these instructions as it will greatly change the look of your project.
To work in the front loop only you insert your hook through the front loop (as shown below), leaving the back loop unworked.
To work in the back loop only you insert your work through the back loop leaving the front loop unworked.
This technique will produce a ridge or a horizontal line across your work and it is often used to create a ribbed effect.