Analogue synths=taking the power outlet into manipulatable sound, more complex the synth more sounds that can be made with it.
There is no truly bad synth also. It literally does not matter unless of course you plan on going very deep into the field.
Digital synths= same in everything but the computer is the soundsource being told to create a tone and such and such and such.
Program is just a graphical interface that is object oriented, involving the mouse to execute commands instead of typing in commands manually like
int create (sin); 350hz or something basically and most of them consist of just knobs and a mod matrix.
Long story short most of digital synths are graphically similar to hardware counterparts with few ones aren't like puredata and Csound while reaktor is hybrid.
Synthesis usual pattern is OSC>FILT>ENV.
OSC edited by anything liek automation/filters/modulation and the envelope/volume being the end result of shaping the sound that goes through the [tunnel] of processes to become a new sound.
Also, there are various types of synthesis.
Subtractive
additive
wavetable
granular[sample based]
phase mod
spectral[Can also be sample based]
TAL synthesizer would be a simple one.
But it would be a good idea to research synthesis and sound design.
There is also a strange little type of synthesis that strictly involves samples, called granular synthesis.