PUT Base Resistors Question
Another PUT question! Is this related to Make electronics - charles pratt - experiment 11 ?

(Example datasheet, which calls the three terminals anode, cathode, and gate)

The theory of operation of these exotic parts is quite complex, but basically those resistors are the "programmable" part. They set a voltage threshold. Once the voltage at the anode goes above the "program"/"gate" voltage, current starts to flow; once that current has gone above a certain small value, the device latches on until the current is turned off again.

I'd avoid them until you have a very solid grasp of the three most common semiconductor devices: diode, BJT, FET.