You are asking a generic question without consideration of any of the real variables such as specific CPU, GPU, PSU, case, ambient temp, etc.
There is no answer without applicable details. Some systems can run from ONE lone fan, others cannot. Since you are a self-described newbie, I recommend you not try to outthink the conventions used to cool a typical system and stick with those, until you have specific reasons to believe you can alter a specific system config (already existing system) for a specific reason.
In general, it is worse to have fewer fans. The fewer you have, the higher the RPM has to be to remove heat from each part, and from entire system . For example, two low speed 80mm fans moving (really moving, NOT the free-air rating which is non-applicable to an actual device implementation) 15 CFM each, 30 CFM total, with have a lower additive noise (perception) than one 80mm fan moving same 30 CFM. Certainly this idea could be taken to extremes beyond any real benefit, beyond a certain # if your parts are still too hot there's usually another case like inadequate heatsink or 'sink-part junction, or those pathetic attempts at stamped-out-metal grills seen in some poor cases.
3 or 4 case fans are seldom necessary, but could be quieter than fewer fans, if the case does't allow larger (like 92-120mm) sizes. Remember that the key is having no dead zones around hotter parts and that the typical case design is such that fans exhaust out the back, making it more beneficial to have ample air intake areas in the bottom front, to passively cool the hard drive (rack).
Beyond that, addt'l fans are added as needed, if other parts aren't staying cool enough. It's also possible that if a case doesn't need fans in all it's potential fan mount locations, that these locations should be blocked off, not just left as open holes (with the exception of the bottom front intake, it's practically always needing to be a passive intake).