At the end of each turn, you add up the IPC value of territories controlled by the side you are playing and you receive that many IPCs. For the UK, in addition to the value of the territories, you get up to 12 IPCs for UK convoys that you can distribute between Australia and India at the end of your turn. The US also has convoys which can add a further 15 IPCs to the US total if they control those.
In AA Pacific, in obtain IPCs for a particular territory, the country must control both the terrritory and any associated convoy route. For examply if Japan holds Philippines, it must also control sz38 in order to get the 3 IPCs for Philippines. If Japan controls Philippines but the US controls sz 38, neither side gets the IPCs for that turn.
I hope this helps.
SS