If you are not playing smoothly it probably means that you are going from one note to another and leaving gaps. This is usually caused on fretted instruments because the left hand and the right hand are not properly synchronised. In other words, you may not be playing the note and holding it on until you play the next note.
If this is the problem, you can do several things.
1. Choose 2, 3 or 4 notes on the same string and play them one after the other smoothly up and down. Look at the way your fings are moving. Spot what is going wrong. Play slowly and evenly.
2. Progress to using notes on 2 strings.
3. Practice scales.
4. Play a short part of the piece you are working on and get it right.
Remember, don't raise the finger that is fretting the note before you play the next note (unless you actually intend for the note to be short).
You could also ask your uke teacher what they mean.