A colon is used to provide a pause before introducing related information.
To make the perfect snack you need three things: bread, butter and strawberry jam.
A semicolon is a break in a sentence that is stronger than a comma but not as final as a full stop.
John calls it football; Sam calls it soccer.
A semicolon can also be used like a comma in lists of items, especially when the list is complicated.
He planned to visit four locations: Sussex, England; Argyll and Bute, Scotland; Mid Glamorgan, Wales and Lisburn, Northern Ireland.