If u don't know how to read or fully understand frames it is ok dont be scared to ask.
here is the main concept:
when you press a button or perform an attack ,the game uses an animation like kicking or whatever attack/special move u did.
Its move has a point in the animation that becomes active as an attack , it is called impact frame a single A attack becomes active at the 10th frame, so we call it i10 meaniing that the impact of the hit comes at the 10th frame.
the outcome of each attack is either to:
1)-be interupted by an enemy attack (which means that the enemy scores a counte hit on you,and your move doesn't make it)
2)-whiff(your attack hits thin air, meaning u are exposed for the recovery of the move or the enemy cleverly avoid the impact of the attack , for example ducking under a high attack)
3)-connects with the enemy and is either
a)blocked by him , or
b)You scored a hit on him.
Now there are some things before we go deeper:
-when an enemy blocks an attack he gets to a block animation(an impact ,like steping a bit back,sparks flying on the air,it depends on the move) ,YOUR char goes to a recovery animation like sheathing the sword back to his belt or steping his feet down after a kick.Both of them depending on the move that got blocked have a preseted animation some times the attacker takes less to recover from his attack , sometimes the person that blocked recovers faster.
This is how we look how a person has advancement after a blocked move or not.
Some examples: You attacked with a move that needs 4 frams to recover after it was blocked,but the defender needs 10 frames to recover from his block-animation(because the attack was very powerfull mostly) that means that the attacker recovers 6 frames faster than the defender.
So the attacker is at +6 frames ,which translates as:" when the attacker recovers the defender needs another 6 frames before the game accepts any of his input" ,which means that u can start to reattack faster than him and his moves will be delayed becasuse he hasnt recover yet , so if u both press A again which is an i10 attack(become active at 10th frame) u will win the exchange since he will start his attack 6 frames after you.
Now dont forget that some moves on block get minus (-4 for example) that means the defender is ready and has the control of his character faster than the attacker.
So a -4 move on block( it is important to remeber it is on block the -4) means the defender will probably win the exchange.
-Lets go now to the on hit properties which is exaclty the same thing, when a move hits an enemy and it is not blocked, the oponent gets a hit animation(it can be anything even a stun) now depending on how fast the attacker that hit ,and the one taking the attack recovers we have again some frame advantage/disadvantage(most hit moves give at least + frames,90% of all moves in the game).
lets take now 2bA : it is -6 on block , +4 on hit , i8.
that means if the oponent defends he gets 6 frames adva., if he takes hitted u get +4 frames adva. the i8 means that it becomes active at the 8th frame of the animation, thats 8 frames after u input the move.
Also take note that even though you might have advancement a move that TC(crouches) will almost always win over a high move no matter the + u get from before.Same goes with other realted staff.
As an aditional note lookat this : PO A is unblockable after a blocked B,[K] becuase the [K] makes the attacker at +8 frames, while PO A come out at the 7th frame ,so since the enemy hasn't yet the control of his char,he cant block.Same with PO B ,2bA.
PS: this is a simple explanation for further info u can look around.
natsu frame data:
https://docs.google.com/spreadsheet/ccc?key=0Ag4-AFwttkImdDZHOVN4VEVfeFFJaEEyRmtHS2FLWUE#gid=0