Making a choice to exercise

I have made a conscious decision to exercise.  I can also make a conscious decision not to exercise.  That is my choice.  What I need to do is to exercise for at least 15 minutes a day.  I need for the exercise to at least make a dent.  I walk around, but I do wonder if that counts as exercise.  I doubt it since there is no real impact made.  So, I guess it means I took a break today.  On the other hand, there are 24 hours in a a day.