hi guys! can you help me understand how multiplexer works..or how it can project/show different numbers in one connection.. Thank you!!

Here is what i mean guys:

 

You just send on port3 what you want to output and turn on one of the transistors for a bit (1-10ms would be fine). Then do the same for the next display, etc. Persistance of vision means you won't see them flashing.
NPN transistors are usually better than PNP but you give them a high voltage to turn them on instead of a low one. To be extra safe 1K resistors in between the PIC and the transistor bases would be good.

 

thank you so much sir!!