Semicolons are used when joining two complete, but related, sentences.
Jane Austen’s novels are wonderful; they are filled with witty observations and colorful characters.
Each of these sentences could stand alone, using a period instead of a semi-colon. This would be correct as well.
Do you have persistent grammar issues? Can’t remember where the comma goes or how to punctuate dialogue? E-mail your questions to me at firstname.lastname@example.org, and I will answer them as part of “Editing for Grammarphobes.” Thanks.