If you don't know how to bend a note on a diatonic harmonica, you'll soon get boring with this intrument, because this is the most popular ,the best and the trickiest technique on the harmonica, along with the over blow technique
Bending note only happens when you draw. At playing a harmonica, you should start with the C harmonica. You can only bend notes at the 1st,2nd, 3rd,4th and 6th holes. Here is the picture wich illustrates possible bend and overblow notes on a C harmonica:
you can see in the 2nd, 3rd, you can bend more than a half step, it depends on how deep is your tounge bending in the middle.
First, let me show you how this works
the Hamonica notes change when you change the dirrection of the air you draw in.
In order to do this, you have to make a special position of your touge and lips. Some people say the best way to learn this technique is saying "Weeeeee", and then say "ooooooo" to bend (of course we just need the mouth position when I said that, you can't actually say anything when you are drawing XD) . If you do this the first time and the note actually bended, then you're better than me!
It took me sometimes to figure out, and what I did is I put the hole a little down, it worked to.
remember this is not how you do it and don't get used to it because this is just for you to understand how it works.
As I said before, you have to bend your touge, and remember to put your tounge always at the middle of your lips so in can dirrect the air.
I found a really nice web site, wich has picture that make you easy to understand, is one of the top web site when you find "bend harmonica" on Google.
so this his how you bend it on the 4th (D to C#)
bend your tounge lower when for a step a step and a half at the 3rd hole:
Pretty hard right?. That is because you've just made your tounge to something it has never done before. Now you've understood how to bend it, it's just the matter of time until you become a harmonica pro. good luck
This is the most difficult technique on the harmonica, others are pretty cool too,like the overblow, it's still a note bending technique but way easier, the easy wah-wah that you cannot miss in a blues song... I'll teach you next time. Have fun practicing!