To begin, if you are going to use it to do a drive then you will absolutely need to prepare a compacted bed for the stones. When using something like paver/bricks they recommend using a 10"(25cm)compacted bed. This is also compacted in a series of layers. Also be aware of how much stone you'll need or have on hand, you don't want to run out.
As far as putting mortar around stone or brick, the stone needs to be mortared onto a concrete bed. If you don't then over time, very little time that is, the mortar will just start breaking part because of the movement in the soil underneath.
When using the stone for walkways no matter how large the stones I have always used some kind of gravel base. The less soil the less heaving and sinking of the stones.
Between the stones you can simply use sand, it acts as a great filler and easy to wash into the joints. It also is graet for planting ground covers.
Hope this helps.
Good luck, Matteow