A public IP is what your ISP gives you to enter the biggest network, the internet. A private IP is what you can configure and it is of no importance if you configure a Class A,B, or C address. Usually we use C class address the one that starts with 192.168.1|.1 the three first octets identify your network, the last number is for your host Pc.

If your ISP has given you a static IP that is great as it will never change and offer better stability.