i downloading it and been walking around and haven't got any message do i need to be at a level or do i need to go somewhere to start it

If it loaded correctly, you should have gotten a radio message and a quest called The Reunion loaded onto your Pip Boy. To start it, go to the Canyon Wreckage, located west-northwest of Primm.

You don't have to be any particular level to start it, but you should be fairly high level - the devs recommend Level 25 minimum.