How does poison actually work?

As the title says I don't get how poison works,
-Is it only applied with main attacks?
-Can it stack? and if so up to how much damage can stack?
-Can special spells like summoner's summons or trickster's clones apply the poison?
-How does the tick rate work, does it apply a fraction every tick or a third every second?
-Does any other stat than poison affect its scaling?

I'd appreciate any bit of info, thanks.

 

its applied with any attack
it doesnt stack
yes
1/3 of your poison stat is applied every second, lasts 3 seconds
no