two resistors in series is for what purpose? two resistors in parallel is for what purpose, resistor and capacitor in series is for what purpose and resistors and capacitors in parallel is for what purpose ???? for any electronics circuit I am asking, thanks

You will often see this in a manufacturing environment where the number of distinct parts available for use is limited because each part is purchased in high volume. Why is this a surprise?

 

circuit diagram is attached for reference. In that I just want to know what's the major difference between capacitors like (c1,c2,c3 etc) and capacitors EC1, EC2,EC3,EC4 etc etc. in any circuit, where can we use capacitors like c1,c2 etc and where can we use capacitors like EC1, EC2 etc and what's the main purpose of these capacitors in any circuit in general? also, in some circuit resistors and capacitors are connected in series, what's the use of resitor, capacitor series connection for any electronics circuit? and in some circuit resistor, capacitor are connected in parallel, so what's the use of that in any circuit?