As the name may have already given away, the Weewah is an envelope filter or auto-wah.
It's housed in an unthinkably tiny enclosure and gives you no hint as to what each of its controls actually does - but that's the fun part. There's often little better creative inspiration than experimenting from the ground up, and that's exactly what you get here - so if you want to preserve the mystique, look away now.
The first knob is a level control, while the second determines the range of the sweep. The toggle switch at the top is the Weewah's secret weapon.
When the switch is flicked down, the sweep is reversed, taking the tone from high to low rather than the other way around. Put the level control a bit lower with the sweep positioned higher, and you'll swap sharp and biting for a throaty snarl that makes your riffs practically leap off the fingerboard in a way that would be tricky to perform quickly on an ordinary wah.
The real beauty of the Weewah is that it's just so responsive and versatile for such a small pedal with basic controls. Paired with a valve amp, you can back off the effect by playing lightly, or saturate by digging in.
That sensitivity is so important to making the effect feel really organic, and keeps this little unit well away from being a gimmick.