I'm not sure what kind of pockets your pattern calls for but to cast on sts in the middle of a row you can use a loop or a cable cast on. When you've worked to the area where you want to cast on sts, just change the needle with the working yarn which is in your right hand to your left hand and cast on the required number of sts. Once you've cast on, you return the needle to your right hand and continue the pattern. On the next row you continue working across the row, working the cast on st as the pattern tells you. You can look at cast on methods under the Free Videos tab at the top of this page under Cast-on if you want to see how to or need a refresher.