How it’s implemented can vary, but you’re gonna take one of three approaches
Microsegmentstion - On a home network this is the hardest but ensures there’s no overlap
Separate VLAN - this is usually good if your router can support it and have multiple gateways for each VLAN. Your router can then restrict traffic. Unifi gear does this well and I use this set up to segment my guest and IoT traffic
Separate subnets - if your router doesn’t support multiple VLANs this can work, but you still need a router that supports it
The latter two can actually work with an unmanaged switch as long as you tag your vlans correctly. The key is having a router than can handle it.