Basic harmonica is not TOO difficult. Don’t worry about reading music. It ain’t necessary.
I would suggest to buy a Hohner Special 20 harmonica. The wooden Marine Bands are great, too, but I find after awhile the wood tends to expand and cut your lips alot. Better to buy a plastic-bodied harp–at least to start.
Harmonicas come in many different keys. Theoretically, you can buy one in all 12 keys, but certain keys are much more difficult to find than others. The most popular ones are probably C, D, G and A. The notes for your full major scale are found in holes 4-7. In other words, if you buy a G harp holes 4-7 are G,A,B,C, D,E,F-sharp, G.
OK, there’s your major scale. However, if you will be playing blues-style harmonica, you will normally not be playing the key of the harmonica. Blues harp is normally played in second-position, also called cross-harp. You need a harmonica a fourth up from the key the song you want to play is in. So if your song is in E (perhaps the most common blues key), you play a harmonica in A. In cross harp, the first note of the blues(-ish) scale will be the hole 3 blow. A popular lick is blow3,draw3,blow4,draw4…it sounds like the first four notes of “Oh when the saints come marching in.”
I’m guessing you’re gonna wanna play bluesy cross-harp, so get that key of A harmonica. If you’re more interested in Neil Young/Bob Dylan-type folky chordal harmonica, get a harmonica in the same key (straight-harp) as the music you’re playing.
Great. Next thing you need to learn is how to isolate your notes. You can either do this with the pucker techique or the tongue-blocking technique. The goal of this is to play clean, single notes. In the pucker technique you, well, pucker your lips to produce a single, small line of air. In the tongue blocking technique you put your lips around three or four holes, and use your tongue to block out all but one hole. Both techniques are useful.
Once you can do that, you need to learn how to bend notes. This is key in producing a bluesy sound. Notes aren’t bent so much in playing straight-harp, but in cross-harp they are essential. Start with the 4draw. Try to make your mouth into a similar shape as when making a “y” sound. You basically drop the very back of your tongue. It’s very difficult to describe, but once you get it, it’s easy. If you hear a drop in the pitch of your note, you’re getting it. Now try to make a smooth slide from the bent note to the straight note. Then try draw JUST the bent note. When bending, it kind of feels like you’re breathing from a different place in your moth.
If you can get the 4draw bend, try the 3draw bend. This one’s a lot trickier…You actually have THREE notes you can bend to. Here’s a good resource for bending info.
The higher notes in the harmonica (holes 7-10) can be bent, but only on the blow notes. Also, you’ll find that each hole has a slightly different position your mouth needs to be in to effect a bend.
And those are the basics. After this, you can learn playing in third-position (also pretty bluesy) and advanced techniques such as getting a solid throat vibrato, hand tremolo, and even overblowing and overdrawing - a technique, which when mastered, will allow you to play a full chromatic scale on a diatonic harp. Jazz diatonic harpist Howard Levy (who also played with Bela Fleck and the Flecktones) is one of the pioneers of this technique.
Good luck! The basics are easy, just have fun with it.