When I'm working in a word document, there are times when I am prompted to use a semi-colon where it makes more sense, to me, to use a comma. From my understanding, it should be used when listing things.

For example:

Lisa had three things on her mind; finding her brother, warning him about the dangers of what he was doing, and getting out of the city before things got any worse. <-------would that be correct?

Can someone clarify this for me?

Apadilla has it right. Here are a couple of examples to clarify further.

1. Lisa had three things on her mind: finding her brother, warning him . . . . [Here we use a colon.]

2. He had a car; she had a bike. [Here we use a semi-colon.]

Example two uses a semi-colon to demontrate the close connection between the two statements. To show a closer connection, this could be written "He had a car, and she had a bike." To break these statements, we can use a period in place of the semi-colon: "He had a car. She had a bike."