I don't about the best way to learn about semicolons, but the way i was taught was basically memorizing it's uses; introducing a list, creating a finishing pause less firmly than a full stop (not sure if you need to use a capital for the new sentence) and coming between two opposing statements to create balance or contrast. i think the best way to learn them, to be honest, is to try and use them whenever possible, though don't go overboard, apparently marks can be deducted that way.
Or, you can always look it up on a website if you're not sure.