This play requires a very awkward body position and one that is not a natural movement, so a lot of practice time is required to get the muscle memory.  There are a few different ways of executing this play so I will explain them and let you choose which feels more comfortable.

You will use this play on balls hit to your left.  Like the play from short stop you are going to field the ball in the middle of your body and use a short arm circle to get the ball to about shoulder height.

The pivot: When you field the ball you will simply pivot your lower half so your hips and feet are point toward second base.  While you are pivoting you will bring your arm up directly behind your ear and about shoulder height and complete the play with a firm throw to the shortstop’s chest.

The knee: As you field the ball using this mechanic you will drop your left knee to the ground rotating your hips and upper torso toward second base.  This is used on a ground ball that stays down and takes you to that position.  If the ball is bouncing or kicks up this mechanic will feel awkward and cause bad throws or indecision.  Again the arm action is short, and you finish with a strong throw to the shortstop’s chest.

Step Back and Open: This is a more advanced play and is used on balls further to your left.  The trick is making sure you have enough time to get the lead runner.  If you decide you do, as you are moving to your left, field the ball is the middle of your stance step your right foot back so your body is square to second base.   You are going to stay low in an athletic position and when you do this your arm is going to stay lower when you step open causing your throw to originate between your hip and shoulder.  What makes this play more advanced is the complex nature of the Step and opening motion along with the sidearm throw.

Keys to every mechanic:

Square your body up to the second base.  Meaning get your hips and shoulder pointed to the bag.

Short arm action.

Strong and accurate feed.

Practice, Practice, Practice.  These are not easy plays so you must work on them a lot.