Your provider can give you an address in two ways: one from a pool for each session (dynamic IP), or always the same one (static or fixed IP).
Dynamic IP
The provider keeps a pool of addresses. When your router connects it gets one and keeps it for a while; after a restart, a dropped connection or a network change it may get another. Most home subscriptions and almost all mobile connections use dynamic addresses. For browsing, streaming and gaming it makes no difference.
Static IP
A static address is assigned to your subscription permanently. It is standard on business lines and usually a paid extra on home lines. It helps when you run a server at home (web, game, NAS, security camera), when a service allows access by address, when you run a mail server (which also needs a matching reverse DNS name), or simply for stable remote access.
CGNAT
Because IPv4 addresses have run out, some providers — mobile operators especially — share one public address among many customers at once: CGNAT. Then you have no public address of your own, cannot accept incoming connections, and port forwarding does nothing. A static IP solves that too. Test whether your connection is reachable with the port checker.
IPv6
With IPv6 there is no shortage, so providers give each subscriber a large prefix (often a /56 or /64) and CGNAT is not needed. The prefix can be dynamic, and devices also change the last part of their address regularly for privacy, so a changing IPv6 address is normal.
Which one?
For browsing, a dynamic IP is enough. To expose a service at home, first check whether you are behind CGNAT: if not, a dynamic address plus a dynamic DNS service is often enough; if you are, you need a static IP or IPv6.