IPv4 in short
In IPv4, the mask separates network bits and host bits. Depending on the prefix, you get network address, broadcast and usable host range.
IPv6 changes the scale
IPv6 uses 128 bits and usually works with prefixes rather than broadcast. The focus shifts to aggregation, routing and block planning.
The calculator helps you see the real range behind the prefix, but operational decisions still need routing, firewall and network documentation context.