Question about small form-factor pluggable ports

I’m hoping someone can help me out here. My networking knowledge and intuition is somewhat limited, and I am trying to understand what exactly a SFP port is. We are using a Cisco Catalyst 2970G-24TS gigabit switch. It has 24 ethernet ports, and 4 SFP ports. I would like to know what these SFP ports would be used for. Specifically, I am looking to add a couple of machines to this switch, and I am wondering if these ports will serve as additional ethernet ports, or if they have a different purpose entirely. Thank you for any help you may have!