i must admit i dont think i have ever used a semicolon; i never correctly have used one atleast. I never really have understood when you actually use them or even what the difference between a semicolon and a comma. but according to SMGTW it is used when you two simalar causes are combined. these situations can be serated by a period but if we are yoto use a smicolon, it shows that the two cause are simalar.

There are many other reasons why and when to use them and this link is a good sourse to learn more.