Newcomers to the harmonica holder generally play some harmonica and more guitar, the challenge being to coordinate the two. To simplify things we start with harmonica parts which require no coordination. Then we try some simple tunes.
Tune your guitar with an electronic tuner, or from a harmonica note (the electronic tuner will usually be better). Then take a C harmonica and place it in the holder. Adjust the holder so that you can play the bottom 3 holes comfortably. These will be the starting point.
Before playing harmonica and guitar together, get the harmonica working by itself. Blow steadily through the bottom 3 holes (holes 1 to 3), sounding like this.
Blow the same holes again, then strum a C chord. Try to end the harmonica and guitar parts together, like this:
Now breathe in the bottom 3 holes, like this:
Now breathe in the bottom 3 holes again, and strum a G chord, like this:
If you are new to the harmonica, more details on getting these sounds are in this introductory harmonica lesson.
The exercises so far have aimed to get a clean harmonica and guitar sound together. Now we introduce some rhythm. Blow 4 times into the bottom 3 holes, draw (or breathe in) 4 times, then blow out once, like this:
Now play the same exercise, this time strum a C chord 4 times with the blow chord, then strum a G chord 4 times with the draw chord, and finish with a C chord, like this:
The same exercise (without guitar) is in the introductory harmonica lesson.
Now try some single note exercises. First review harmonica tab and single note playing by visiting this harmonica lesson. The lesson considers holes 4 to 6, the first half of the C scale. Now strum a C chord, and, following the tab from the lesson, play the notes 4B 4D 5B 5D 6B. It should sound like this:
You are playing the first 5 notes of the C scale along with a C chord on the guitar.
Now we practice guitar chord changes. Play the same pattern 4 times, while strumming a C, Am, F and G chord, like this:
Now try a simple melody with guitar. Start by learning the harmonica part to Kumbaya available here. If you need the guitar chords to Kumbaya, they are here. Try playing the tune with guitar, like this:
Simple harmonica parts sound great with guitar, if they are played well. Simple but safe is a better strategy than attempting complex harmonica parts that you don't quite get. Audiences always prefer good execution to good intentions.
Playing harmonica and guitar together is like riding a bike. It seems impossible until you get it. With practice this skill becomes much easier.
To extend the harmonica/guitar repertoire most players need more harmonica skills. The harmonica lessons on this site will help. Try learning some more harmonica tunes, and visit the harmonica course at a glance page for more details on harmonica technique, particularly for blues.