What is the difference between a PUT and a normal transistor?
As far as I know these are completely different beasts (and a simple google search agrees).

The built-in negative resistance of the unijunction transistors is what makes them attractive (or maybe "cute" is a better word) in "simple" oscillators but IMHO you will be better off building a 3xRC (\$180^\circ\$ phase shift network) oscillator on one normal bipolar transistor or a simple oscillator on an op amp. Almost nobody uses negative resistance devices nowadays.

Negative resistance is fairly common in nature (a humble spark gap has this property) so this may be the reason why historically they were used for intro level oscillators. But there also were times when people notoriously made their own rectifying diodes out of some kind of rock and a piece of wire so they could build a long-wave radio receiver, so... :P