Stretching is important to your body before you exercise.  It is the warm up for your muscles.  When your muscles warm up slowly through stretches they become flexible.  Exercising without a properly warming up the muscles will result in injury.  It is important that you hold your position when you stretch.  Bouncing and rapid movement during the stretch can do more harm than good.  Move slow and steady.  Here a few sample stretches to get you started:

TOE TOUCHES:                            BEHIND THE BACK:                                NUMBER 4s:                                             BUTTERFLIES:

Keep your legs straight.                     Put one hand on your opposite                    Reach with your opposite arm towards                  Put the bottom of your feet

Don't lock your knees.                       shoulder blade.  Use the other hand            your toe.  Fold your other leg in with your               together.  Hands on your toes.

Reach slowly for your toes.                 to brace your arm at the elbow.                toe touching the outstretched leg below the                Push your knees down

                                                            Switch arms and repeat.                            knee.  This makes your legs form a #4.                    with your elbows.         

                                                                                                                            Switch arms and legs and repeat.

Hold each stretch to the count of 10.  If you don't know how to count slow.  Count one-one thousand, two-one thousand, three-one thousand, etc...  then relax each stretch for at least 5 counts.  You should do at least 5 repetitions of each stretch.  So for Behind the Backs and Number 4s you should do a total of 10.

Here are some links to other stretches you might want to try to incorporate into your routine:

HGTV Stretching    Runner's World Stretches for Kids    Stretching Routines  Young Women's Health Stretches