This is to help you learn the very basics without the expense of all the tools.  To do this professionally, you will want to invest in the tools.  However, as a fun crafting experience, this will allow you to learn the basics.

Glue the front to the back.

You can use rubber cement that you can find at any craft store or Walmart.  Double sided sticky tape is good to use for hand-stitching, but not for a sewing machine.  Place the tape on the back side of the leather where you want the pocket to be placed.  Peel the tape cover.  Adhere the pocket to the envelope piece.

Mark your holes.

You can use a sharpie, ink pen, or the tip of the scissors to mark your holes. Hold your ruler in place while marking the holes to be sure they are equal distance apart. 

Punch your holes.

With your rotary punch set on the smallest setting, punch a hole right where you placed your mark.  Try to center the mark in the center of your punch.

Choose your stitch.

The simplest stitches are the running, or straight line stitch, and the overcast stitch.  Both can be done with a single needle.  Once you have learned the basics, you can begin to work on more complex stitching and also create your own. 

Create stitched embellishments.

Decide how large you would like your splash to be.  

Mark your center, then mark one point to the left and another equal distance to the right of your center mark. (1)

Using your center point, mark one point to the top and one to the bottom the same equal distance as the piece on the left and on the right. (2)

Mark one point in the middle of each of the 4 points. (3)

Once all holes have been marked, use the rotary punch on the smallest setting to punch your holes.

Stitching your embellishments.

From the backside of the leather, start your needle and thread in the center hole.  Leave enough thread to tie off at the end of your stitching.  Order of stitching:

1 to T2, back to 1.  

1 to RT3, back to 1.

1 to R1, back to 1.

Keep this pattern until you have gone completely around.  If you would like the thread of the design to be thicker, repeat the steps.

On the last stitch, tie the thread end in a knot with the thread beginning.  Melt the end of the thread with a lighter to better secure the knot.

Punch holes for closure and finish product.

Using the largest setting on your rotary tool, punch a hole on the point of the V. Fold this over the front pocket to determine where you would like to place the peg screw closure. Using the tip of the scissors through the large hole on the V, mark the location. Using the second largest setting on your rotary tool, punch a hole. The screw will be on the inside of the pocket area and the peg on the outside of the pocket.