ixed EQ's are about as basic as you get - you'll often find these on cheaper / smaller mixers and they're designed to tidy up the sound rather than make delicate adjustments (think of fixed EQ's like a big old paint-brush). Fixed EQ's will be set to certain frequencies (on my Behringer MX3282a, the 4 stereo channels have Fixed EQ's set at 80Hz, 500Hz, 3KHz and 12KHz) - you can not change the frequencies at which Fixed EQ's operate. Fixed EQ's will only have one knob which sets the desired amount of Gain at the frequency labeled on it.
This image shows the typical layout of a fixed EQ on a mixing desk - not this arrangment has 3 bands, Hi, Mid and Low, to cut or boost these frequencies, you simply turn the knob left or right respectivley