Is it true that a semicolon cannot be used to join an incomplete sentence and a complete sentence?
The most common way that semicolons are used is to connect two independent sentences that are somehow related or connect two ideas.
The less common way that semicolons are used is in lists in place of commas if the separate items of the list contain commas themselves. This might look something like:
"She asked the following people for help: Kate, her neighbor; Steve, her mailman; and Doug, her bus driver.