Semi-colons can be used to connect two independent clauses. For example:
I enjoyed the movie; it is one my favourites.
A simple way to think of when to use a semi-colon is that one can be used in place of a period between two sentences when these sentences are closely related.
Note that a capital letter is not used immediately after a colon (unless, of course it is for a proper noun)
Beware of using a comma instead of a semi-colon or instead off a period.
Other examples of when to use a semi-colon include:
Flora was awarded eight prizes; Jennifer did not get anything.
The friends gathered for a house party which was the last time they ever got together.
The friends gathered for a house party; it was the last time they ever got together.
David absolutely loved Paris and had visited Paris, France; Paris, Texas; and Paris, Ontario.