First thing you will need to do is get yourself
a "C" Harmonica ( aka C Harp)
This is the best and easiest key to start learning on and most of the resources online
will suggest you use a C Harp to start off.
Listen to as much harmonica as you can
Practice as often as you can.
Collect your favorite players and songs
Listen to them over and over again.
Try to copy the riffs, techniques, by playing along with them
Check out the Online Resources.
There are a variety of styles for playing diatonic harmonicas which are often referred to as positions.