@Bailey-Hines
In brief:
In case at least one warship of a power you are at war with is in a sea zone marked with a Convoy symbol adjacent to one or more of your controlled territories, you are subject to convoy disruption during your Collect Income Phase. This is resolved by special dice rolls per enemy warship and results in IPC-deduction - but is limited by the IPC-values of your adjacent territories.
The rulebooks have that explained in detail.