Each broadband or fibre router, when it connects via its service provider, will be allocated a WAN IP, from a range of numbers allocated to that particular provider - a Public IP. The provider can give you a dynamic Public WAN IP address, but exceptionally some allow you a fixed or static address. Everyone connected to your internet service via your wired or wifi LAN, will show to external services that WAN address. So any posting you make to any forum, will include your WAN IP address, even dynamically allocated IP's tend to stick, especially if your router is left on 24/7. I have a range of special WAN IP numbers permanently allocated to me, in the 44.xxx.xxx.xxx range. Plusnet has IP's beginning with 51.?.?.?
It is possible to disguise or spoof your, by running your connection via VPN, or Virtual Private Network. VPN servers act as intermediaries, translating your genuine WAN IP to another IP, but you pay for the service.
Your router allocates internal LAN IP addresses. Again these can be static, or dynamically allocated IP addresses. So I know what IP to print to, I have my printers on static addresses. Likewise with an IP camera. Internal LAN IP's are usually in the range of 192.?.?.?. or 10.?.?.?.