The important part to learning a fighting game is figuring out all of the attack and defensive options in a game.
For example take a game such as Tekken.
Ways to attack are high, mid, low and throw.
Ways to defend are guard high, low, sidestep, 8 way, back dash, reversal, parry.
Attacks all have different properties such as their advantage or disadvantage on guard/hit.
Does the attack launch, knockdown, wall splat, slam down, cause a stagger?
And then you have ways to counter your opponents defensive option.
Opponent guarding high? Hit them low
Opponent guarding low? Hit them middle
Opponent sidestepping or 8 waying? Use a tracking or homing attack
Opponent backdashing a lot? Use an attack that has long range or get near them via dashing or running.
Opponent using Reversals or Parries? Use a knee/elbow/head attack because those can't be parried.
Opponent using certain attacks in a range to keep you out? Move in and out of that range to cause a whiff then punish.
Fighting games are all about finding the option to stop your opponents option.
When it comes to determining which characters are top tier its all about seeing which character makes the most out of choosing the correct options.
For example Bryan. Great keep out game with 3+4, good lows, tracking attacks, whiff punishment, wall game, combo damage, single hit damage, pokes, mids. He has everything. His only downside is that his punishment when guarding attacks that don't have a lot of disadvantage for their risks such as a hop kick is only like a 1,4 which isn't much it gives advantage but its not as juicy as a knockdown punisher. That is just an example, but that is minor compared to the rest of his tools that he possesses.