The A button will perform a weak attack. These are usually faster than, but will not interrupt strong attacks. Weak attacks can be used to prevent the opponent from infighting, as this will not happen while you are in the animation for a weak attack. Weak attacks can be parry cancelled. You cannot KO the opponent with weak attacks, and without infight you cannot KO with a combo that had a weak attack in it.
The B button will perform a strong attack. These can only be interrupted by other strong attacks (most specials and supers included). Without infight, strong attacks can only be cancelled into specials and supers.
Pushing C puts your character on the defensive. For a short time incoming attacks will be evaded, and if you continue to hold defense you will begin to guard instead. For a moment after being infighted or blocking an attack you cannot evade. If you continue to guard against an assault, your guard may break, which will result in you being stunned and your character sprite will temporarily turn a shade of grey.
Entering defense mode just before an attack connects with your character will cause you to dodge the move. Your character will flash white and usually enter a dodge animation. You aren't able to evade for a short time after being infighted or guarding. If you evade a strong attack the opponent will be slowed temporarily, allowing for a counterattack.
8C or 2C will perform a high or low parry. If the timing is right and the opponent strikes your parry, your character will perform a counterattack of some sort. More information can be found on the parrying page. However, if you parry the wrong way or fail the timing, their hit will become a counter hit.
If you are hit with a strong attack while performing an attack or parry, that counts as a counter hit. Counter hits add bonus damage in proportion to the strength of the attack. If you score a counter hit on somebody, your attack can be immediately cancelled into another attack. Counter hits also induce a lengthy hitstun, allowing you to pull off certain attacks or setups that take time, or run behind to back stab them while they are vulnerable.
Hits from behind will backstab, or "back stub" as it says in the game. Back stabs add slightly more bonus damage than counter hits and you can both back stab and counter hit with the same attack. Backstabbing and counter hits are the only ways to put an opponent into heart break.
Pressing a button when taking damage is called resisting. Resisting will both reduce damage as well as end the combo sooner. Pushing A or B performs Type-A resist which focuses on reducing damage. Pushing C will perform Type-B resist which focuses on recovery time.
There is a limit to how long the game will let you combo. Because of this, many simple loops and such that seem to be infinites will whiff after a certain point. Until the combo ends and the opponent is able to take action again, any further attacks will not harm them. Since this is not displayed in the game, it becomes almost intuitive to know when you are reaching this point. It comes sooner if the enemy resists well, and may be prolonged 1-2 hits with an assault infight.
Pushing A, B, or C when wallslammed, groundslammed, or in the air and the opponent's combo limit is near will attempt to recover. You can hold left or right to choose which way to move upon recovery. For a short time you will be invulnerable, but while falling or landing you will be at risk. It is best to have a plan when attempting recovery as doing it haphazardly will most likely only serve to reset the opponent's combo. If a combo is "invalid" that means the opponent could have recovered at some point. Choosing not to recover can be safer as your defensive options are better on the ground.
Dashing into your opponent while holding forward will infight them. While there aren't grabs in GoF, infights are the primary method to punish people on the defensive. When you do this to somebody, their character will become stunned for a moment, allowing you to combo them. Also there will be a timer displayed over your character. While this is active, your combo potential expands. Strong attacks may be cancelled into other attacks fluidly. Strong attacks can also be parry cancelled while in infight. Also, while weak attacks still cannot KO, they will no longer prevent a KO when used in a combo. In other words any strong hit during infight can KO the opponent. On the other hand, if you have infight activated and are wallslammed, you will be KO'd even if the opponent who didn't have infight started a combo from weak attacks. As of version 18.104.22.168, if your infight timer runs down and you are close (less than 200 measure) to your opponent, it will linger, flashing at 00:00.
Pushing 6CC after an attack performs an assault infight which requires 1 meter. If your strong attack was parried and you do this, the opponent will receive the same stun as when being infighted. It is also a good way to recover if your attack was evaded, allowing you to block, evade, or otherwise respond to your opponent's actions towards what he thought was a vulnerable opponent. Activating assault infight is used offensively mid-combo to KO opponents in the case that your combo used weak attacks, requiring infight to KO.
Holding back or forward will influence the amount of knockback you receive from being hit. Depending on the opponent's combo, you may be able to place yourself out of range of their next attack.
Pushing 4CC when being comboed or infighted will burst, wallslamming the opponent. Bursting requires 1 meter but in some cases can take 2 away. After bursting the character icon under your health bar will flash blue and display "COOL DOWN". While in cool down, you may not burst again. This lasts for quite a while, so don't expect to be able to burst just because you have meter stocked up.
Endurance affects the speed at which you recover from attacks. Certain moves may not combo if the opponent has high endurance, and others may require the opponent to be in heart break. Endurance replenishes slower while guarding, and pauses while blocking, evading, or taking damage. Generally, weak hits deplete 10% endurance and strong hits 75%. Some attacks do not damage endurance. Blocking a weak hit is still 10% and blocking a strong hit takes 50% endurance off. Attacks that hit multiple times will take that much endurance away per hit, although you cannot go below 0% without being back stabbed or counter hit.
If a back stab or counter hit puts you into negative endurance, you will enter heart break mode. While in heart break, the meter will slowly go back to 0%, at which point endurance is refilled at 100% and stays there for a short time. Blocking or being hit will momentarily stop the heart break meter. While in this state the victim suffers severe recovery time from hits taken, and is unable to parry cancel or burst.