Hi Ayeesha,
A good way to start is too read the documentation.
Check the documentation on mobility :
If you are still unsure in how to use the mobility module,
I recommend you to compare the mobility of different examples.
Mobility can be set either using helpers or without them.
You can see an example of a gridMobility and 2 nodes set with a constant mobility (without helpers) in the
src/lr-wpan/examples/lr-wpan-bootstrap.cc
I hope this helps