I read a lot of self-published work. Punctuation is a major issue in works that have obviously not been vetted by a competent editor. Be honest. Do you know when to use a semi-colon and when to use a colon? Do you even know the difference? This is a colon : This is a semi-colon ;
Got it? Okay, let's move on. Colons are used to define time or a list.
The menu offered three different sauces for pasta: alfredo, marinara, and bolognese.
Semi-colons are used like commas (note they have a comma in them!) to separate independent clauses or in the place of a comma when commas are already used to differentiate a group.
Ron packed up the bats; Charlie herded the kids into the station wagon.
Jeremy introduced me to his sister, Pam; her husband, Lou; and their son, Robin.
**Note that by using the semi-colon in the above sentence, I've clearly shown the reader that Pam is Jeremy's sister and Lou is Pam's husband. If I'd just used commas, I could have been discussing four people instead of two: Jeremy's sister, Pam, Pam's husband, and Lou. (And look! I used a colon to define the list. Dang, I'm good!)
Still confused? Don't sweat it. But before you hit "upload," make sure you've got a really good editor to clean up these pesky little issues!