A semicolon is a punctuation mark used to connect two thoughts or ideas which are somehow similar. Generally, each thought or idea could be used as its own sentence, but the flow of the work may be interrupted by the short, choppy sentences.
Semicolons are a little archaic and are not necessary in modern writing. Even in formal writing, they may be replaced by a comma or a period. However, if they are used properly, semicolons can add a pleasing continuity to your work.
When reading out loud, we pause for semicolons much the same way we pause for a comma.