The harmonica is one of the easiest (and most inexpensive) instruments you can buy. It is a great and easy way to get into music even if you don't have a musical background.
You asked if there is any difficulty on learning the harmonica? I'll be honest, there will be some difficulties when you start. You can't learn any instrument without facing any hurdles at all. However, compared to other instruments (guitar, piano etc), the harmonica is definitely one of the easiest to learn. You will be playing songs within a few days (or even hours)...it's that easy!
So, if you are interested in music, and want to take your first step, there's probably no better way than to start with a harmonica. My harmonica lessons will make the learning process very easy (and enjoyable) for you.... Guaranteed :-)