I guess I'll explain it a little less technically than omegaryuji (who did a good job explaining, btw) and throw in some real world applications/uses.
Hitstun and blockstun are basically states caused to a character when getting hit or blocking an attack, respectively.
Hitstun is particularly notable in the combo process. Ever notice how some combos work when starting with a heavy attack vs a light attack? That's because the attack initiating the combo either does or does not provide enough hitstun. Light attacks don't always "stun" on hit long enough for a follow up to connect, while heavy attacks usually do. Hitstun can only be canceled by mechanics such as combo breakers or bursting, which is not present in KOF.
Blockstun is a bit more technical in the sense that you don't necessarily always see the effects of it outright. As omega explained, when an opponent blocks your attack, they are locked in a blocking animation for the duration of however long your attack causes blockstun (which is generally denoted as being either positive/negative X amount of frames on block). At this point, even if your attack animation has ended but causes a large amount of blockstun, this puts you are quite an advantage. For example, CD attacks generally cause a large amount of blockstun. A general tactic is to pressure a defensive opponent using hop CD attacks. The reason for this is because once the opponent is locked in blockstun, you recover from your attack before they have a chance to retaliate, letting you lead in with the mix-up of your choice. Unlike hitstun, KOF has 2 systems to combat blockstun: Guard Cancel Roll and Guard Cancel Blowback.
Tick throws and frame traps are large examples of this.
When an opponent is in hitstun, they generally cannot be thrown, unless it is a comboable throw, and they can never be throw while in blockstun. For example, if you were to force an opponent to block a heavy or CD attack and attempted to throw them even with a throw (even command and super throws), it would whiff. However if you force them to block a light attack, it generally doesn't cause enough blockstun for protection against throws since the duration is so short. Tick throwing is a mix-up tactic employed by taking advantage of blockstun fundamentals and frame data.
Omega didn't go over it, but attacks generally have 3 stages: startup>active>recovery. Frame traps are blockstrings that utilize blockstun and the 3 stages of attacks. Let's say you have a mirror match between two characters. If they jab on the same frame within range of each other, they will trade hits. This is where blockstun factors in to frame traps. Using the example mentioned earlier, causing blockstun with a heavy or CD attack, the opponent is now in blockstun and you have recovered. This scenario in mind, if both characters were to attempt a jab, the attacking character would win and not trade as previously mentioned. This is because the attacking character has the frame advantage while the defending character is still in blockstun. Because the attacker gets to initiate the attack while the defender is still recovering, his jab would win because his attack would have reached the active frames of the attack while the defender is still in startup frames (period of time in which the attack does not yet have a collisionbox nor can cause damage) of his own attack. This is the essence of a frame trap: setting up a situation in which the opponent has a window to attack (no longer in hitstun or blockstun), but their startup>active frames are not quick enough to retaliate without being counterhit.
However, I won't go into more detail unless you have more questions. It tends to get quite complicated to explain the more you ask how hitstun and blockstun are integrated into the overall flow of combat.
