How does pillage work?

What does the above highlighted field mean? and what they do?
Does pillage work on unit if i change the "targets allowed" from structure to units?

Chaning allowed targets to include units will give gold for attacking units.

Accumulation Step = 1
Salvage Cost Ratio = 0.50

What does the above mean? How much does it get per hit?

All I can say with authority is that changing the Accumulation Step to 0 will cause your map to crash in-game.

Im not sure about accumilation step but I'm fairly certain that Salvage to cost ration is like this. You have a building that costs 200 gold and 0 wood (hypothetical) and a grunt that does x damage, when the grunt finally kills the building, he/she will have gained 50% of 200 which is 100 gold. The gold per hit will depend on the damage the grunt does, health of the building, cost of the building and Salvage Cost Ratio. You can take the hp/dmg and that will be the number of hits, then you can take the cost*SCR/number of hits to get gold per hit. The final forumula would look like this:

(cost*SCR)/(hp/damage)

If you feel you have learned from this, some rep would be nice.

oh so it is not affected by damage?

Read carefully.

yes it is, you gain Salvage Cost Ratio*(% of building's hp dealt) per attack.

I'm not sure but I would think Accumulation Step was how much the amount of resources gained increased, so you would gain resources faster the longer you were pillaging, or you would gain more resources the lower the hp of the building. For example, if Accumulation Step was 2, and you dealt 1% of a building's hp per hit, and the building cost 200gold and the SCR was 50%, first hit would gain you 1 gold, second hit 2, third hit 4, fifth hit 8, etc. OR you would gain 1 gold at first, when the building was on 50% hp you would gain 2, 25% you'd gain 4 etc. I think the first one is more likely.

I believe accumulation step is the amount of gold you will receive at one time. For example, if it is set to 1 and the formula comes out to say you earned 1.3 gold, it will give you one gold and keep the .3 hidden somewhere, then if you get 1.7, it adds the 0.3 and gives you 2 gold.

If you set it to 5, you wouldn't get gold from pillage until you've earned at least 5 gold. If you earn 7.3 in one attack, it gives you 5 gold and keeps the 2.3 extra around, and if you do 7.3 again, it adds the 2.3 for 9.6 total, then gives 5 and keeps the leftover 4.6 around. If you then earn 5.4 gold, it adds the 4.6 to get 10 total, and gives you 10 (because it is a multiple of 5)

I haven't tested this theory, though