In the upper right corner of UTAU is a button labelled "Mode 2". When it's not pressed, you are in Mode 1. Right click a note to edit pitch or use the shortcut ctrl+T to get this window:
It is much easier and more common to use Mode 2 for editing USTs. When you right click on a note to edit pitch, or use ctrl+T, you will see this window:
From here you can add portamento and vibrato. You can add more control points to portamento from this window in order to create more complex pitchbends. Alternatively, once portamento is enabled, you can right click on existing control points to add/remove points, as well as change the shape of the connection between points.
