A semi-colon is used to join two sentences when they are very closely related and a conjunction becomes too wordy.
1) In place of a coordinating conjunction:
She loves me; she loves me not.
They say it's your birthday; it's my birthday too! - Paul McCartney
Management is doing things right; leadership is doing the right things. - Peter Drucker
2) Along with a conjunctive adverb:
Sometimes mistaken for a FANBOY, a conjunctive adverb actually joins two sentences with a semi-colon AND has additional punctuation inside the second sentence.
I hate spinach; however, I love broccoli.
I want to graduate with honors; furthermore, I want to go to law school.
I don't want to go out tonight; besides, I have homework to do.
Some common conjunctive adverbs include accordingly, also, however, furthermore, nevertheless, consequently, finally, likewise, and meanwhile.
3) Semi-colons are also used to separate items in a series when the items themselves contain commas.
Some important dates in US history are July, 4, 1776; December 7, 1941; and September 11, 2001.
4) A colon emphasizes what comes after it when a comma isn’t enough to set off the next part of the sentence.
To introduce a long list:
The baker gathered supplies for the competition: flour, sugar, eggs, butter, and milk.
To introduce a long or formal quotation:
The preamble of the Declaration of Independence guarantees these rights: that all men are created equal, that they are endowed by their Creator with certain inalienable rights, that among these are life, liberty and the pursuit of happiness.
To introduce an explanation:
My sweetie canceled our date for a really stupid reason: to go to the game.