I come from the background of a flute player, so I can read sheet music. However one thing that has me scuppered is one of the notations on the Ukulele sheet music.
On a lot of them they have chord references above the bar, and above a note which is not the same. For instance in this example, in the 4th bar an F sits above it, but no F is actually in that bar:
http://capotastomusic.blogspot.co.uk/2011/10/o-come-all-ye-faithful-adeste-fideles.html
So what does it mean when there is a chord reference in letter form above the bar?
That's typically the guitar/uke chord you would play. It's ok to have an F chord and play an F note in the melody, and then there is a C chord and a G note in the melody. Chords and Melody are different parts of the music, and do not have to be unisons or octaves in order to satisfy the construct of the song.
As a flute player, I do not think you play chords, so you are probably just following a single melody line, but for someone who wants to strum and sing, in the absence of a (second) treble and bass clef (to actually spell out the chords in notation), they will use the chord name above the staff for what to strum, and then the single notes or tab lines for the melody notes to sing. The way this 'Adeste Fideles' is written might also be considered in the style of a 'Fake Book' which assumes you know how to finger basic chords, and many sheets will have chord diagram at the top that shows the chord pictograms indicating string, finger position, and fret position for the intended chord.
For those that do not sing, but are a more advanced player, they can play an arrangement with both the chords AND the melody line, all on one instrument. This is called 'Chord/Melody' style, and is VERY common on ukulele, guitar, harp, dulcimer but less common on bowed instruments using double-stops, such as those in the violin family.
Please let me know if this helps. Hopefully others here on UU will chime in if my attempt to explain does not help you.