Summarize this article:

The apron, also called a scürze, should cover the seam on your dress, which should hit at the narrowest part of your waist. There will almost always be a small button on the dress and a small loop inside of the apron to secure the pieces together. The most common way to tie your apron strings is with a basic bow. Loop the left tie, then bring the right tie over and around the left loop, creating a second loop. Push the right tie through the second loop you made and pull it tight. The side where you tie your dirndl apron implies your relationship status, so pay attention to where your bow sits! If your bow sits on the left side of your waist, it indicates to potential suitors that you are single and open to flirtation, so be prepared to get a little attention if you choose to tie your dirndl this way!  If you are married or in a serious relationship, or if you just don’t want to catch the eye of any young men in the crowd, tie your dirndl bow on the right side.   Bows tied in the center front are reserved for very young girls, although it traditionally meant that a girl was a virgin.  Bows tied in the back to indicate that a lady is either a widow or a waitress.

Summary:
Place the apron at your natural waist and button it to the skirt. Wrap the apron ties around your back and make a bow in front. Tie the bow on the left side if you are single or the right if you are taken.