1. We sometimes use a semi-colon instead of a full stop or period. This is to separate sentences that are grammatically independent but that have closely connected meaning.
Josef likes coffee; Mary likes tea.

Tara is a good speaker; she speaks very clearly.

You did your best; now let's hope you pass the exam.

Ram wants to go out; Anthony wants to stay home.

Note that in the above examples it is not correct to use a comma instead of the semi-colon.

2. Use a semi-colon as a kind of "super comma". When we have a list of items, we usually separate the items with commas. If the list is complicated, we may prefer to use semi-colons in some cases.
ABC Investments has offices in five locations: Kensington, London; Brighton & Hove; and Oxford, Cambridge and Manchester.

Rental cars must be returned on time; with a full tank of petrol; in undamaged condition; and at the same location as they were collected from.

http://www.englishclub.com/writing/punctuation-semi-colon.htm