First time flyer. Southwest questions?

I will start making flights between San Jose and San Diego several times a year for college and I've never flown without a group before. It will be mostly short travel periods so I will only have a carry on every time. I heard you can check in online 24 hours before hour flight. How does that work? If you check in online 24 hours before does that mean I don't have to check in at the airport? And if so, do I just have to go through airport security and straight to my gate since all I will have is a carry on? No one is my family is a flyer so any other tips and information about southwest airlines wou.d help.