Generally if your radio is SXM ready then there is not much more to plugging it in and mounting the antenna.
What model radio do you have and does it say SXM ready on the front and or in the manual?
The antenna is always best mounted outside but it can be located on the dash if it has a clear line of sight of the sky or under a fiberglass top. You cannot mount it below anything metal as the signal cannot get through to it.
2001 F250 Superduty
2 Crazy Huskies