Uh? Can I have an example for that...?
If you create a block against any and all actions, then any attemt to act at all can be used to break said block. Whether it's an attempt to move, or shoot, or dance, or whatever. If you roll high enough the Block will be broken.
If you create a block to hinder movement, then only movement will break the block. On the other hand any and all actions that aren't movement, that is an attempt to change zones, will be unhindered by the block.
The same for a block against attacks, only attacks will break the block, anything else won't break the block, but will not be hindered by it either.
There are of course countless levels and combinations between a "block against 1 kind of action" and a "block against all actions"
As for action reduced by the block:
Take movement for example.
A has established a movement block of +3 to hinder A's movement
A wants to move and rolls a +5 for that purpose.
Normally A would be able to move 5 zones with that roll. But there's a block in the way.
The roll of +5 overcomes the block easily, but the movement is reduced to 2 zones, since only 2 shifts remained after the block.
In case of an attack block.
A creates a block to prevent B from attacking. The Block is +4
B Attacks and gets a +6
A now has to contend with being hit by 2 shifts plus the damage from whatever weapon B was using.
A can still roll defense against B's attack. However The defensive measures
do not stack you always use the higher defense, while the lower has no effect at all.
Attack +6
Block +4, Defense Roll +3 -> Total defense +4 -> Shifts suffered from the attack 2+Weapon
Block +4, Defense Roll +5 -> Total defense +5 -> Shifts suffered from the attack 1+Weapon