At the top, the instrument name can be tapped to open a list of the 34 instruments. Alternatively, you can use the arrow buttons to navigate to instruments.
At the top right, you can find buttons for Help, Setup, and MIDI Panic (stops all notes).
The dynamics display provides you with visual feedback on the currently playing dynamic, which can be controlled via the note velocity or the mod wheel (for sustain and legato articulations). The instrument icon is displayed below the dynamic.
In the center, a row of buttons allows you to select an articulation. The number of articulations depends on the instrument. Some instruments have no articulation.
In the parameter section at the bottom of the panel, you can make adjustments for the selected articulation, as well as for the main volume.