Content in “circuit”

Like many here, I were in need of a bit of amplification of a weak signal. This signal had "low impedance", I suppose. The supplied circuit diagram shows two different ways of meeting my need.

The left circuit uses a NPN transistor. The right hand circuit uses a PNP transistor. I chose the one with PNP. Quite "arbitrarily". The BP103B is also known as FA300.

I have a fairly strong background in code development, but I would like to build a stronger knowledge in curcuit design. I can read a datasheet and learn how to hook up a certain component, but when it comes to using a specific component for a use other than it is designed for I lack the knowledge to know when to use a capacitor, flyback diodes, etc.

I'm not positive this is the right place to post this.  Admins please move it if I'm asking in the wrong place.

I have a circuit digram but i cannot understand it. can anyone help me explain?

Pjnai123