The first step is to cut a piece of cardstock in half so you have two pieces that are each 8.5"x5.5". Fold them in half to make a card shape. (Of course, you can use any size paper for this.)
Once you have the paper cut, you can draw your heart. Do this on the inside of the card so that the pencil marks won't show. Don't worry about getting it perfect, since you can't really tell when it's all just string!
Add dots to the line, then start threading the heart!
I found it useful to punch all the holes with my needle first, so I could see them from the other side (where the threading was happening). Just make a design that looks good to you! If you don't like it, you can always pull out some of the thread and try again.
To finish the card, glue the second piece of paper to the inside to cover up the back of the heart. Write your message, and gift!