What is the purge canister and what is it for?

Is it an emissions thing?

I think what it dose is builds up the fumes from the petrol tank and when full, purges into the intake manifold

I think

lol i should have tried wiki first

A lot of people seem to have trouble with them, why do they cause so much trouble when they appear to be so simple?

at what point does the car draw the fumes in from the cannister?

why doesn't they engine draw air in from the cannister all the time? (does it interfere with mapping?)

when the fumes are being removed from the cannister, does the cannister draw air in from the air box (filtered air)?

does it ever need replacing? if so how often and when? how will i know to change it if i don't want to pay a mechanic to read from the ECU and tell me the fault codes?

what will the car do if there is a fault with the solenoid or the canister?

i put it to you all to answere these questsions, thank you all