Semi-colons (;) have two common functions. First, a semi-colon is like a weak full-stop and separates two closely related sentences, e.g. It is raining heavily; we can’t go out.
Second, a semi-colon is used in a list instead of a comma where one or more of the items contains a comma, e.g.
When you go to the shop, please buy me the following things: a loaf of bread, margarine, Vegemite and a bottle of milk.
>> When you go to the shop, please buy me the following things: a loaf of bread; margarine; Vegemite, not Ozemite; and a bottle of milk.