Answer:
I begin and have no end. Eventually I will be the end of all that has begun.
I am an activity dogs are very good at when a ball is thrown.
I stay where I am when I go off. What am I?
I can be simple or I can be complex. I can be found in this riddle or in everyday life. I can be shapes or even colors.
I am a portal to another world which you cannot enter. Only you can see me but I can't see you.
The answer I give is yes, but what I mean is no. What was the question?