A network connects applications
A network lets devices exchange data using shared rules called protocols. A host is an endpoint such as a laptop, phone, printer, or server. A client application requests a service and a server application responds. These are roles: one computer can act as a client for one conversation and a server for another.
A local area network (LAN) connects devices within a limited area. A wide area network joins networks over greater distances. The internet is a network of networks, while the web is one service that uses it. A working Wi-Fi connection therefore does not, by itself, prove that a website is reachable.
Follow the devices on the path
A switch forwards Ethernet frames within a local network, learning which source MAC addresses appear on its ports. A router forwards IP packets between networks using its routing table. An access point connects wireless stations to a network. A home broadband box often combines routing, switching, Wi-Fi, and other services, but these are still separate jobs.
Draw each hop when investigating a connection: laptop, access point, switch, router, remote network, server. A failure at any stage can prevent the application from working. Begin with the nearest dependency instead of treating every problem as an internet outage.
Who should receive the message?
Unicast is delivery to one destination. Broadcast reaches the local broadcast domain, as with an Ethernet broadcast ARP request. Routers normally separate broadcast domains. Multicast targets a group of receivers rather than every host; delivery depends on membership and network configuration.
These categories describe intended delivery, not trust. A unicast message can be unwanted, and a broadcast can be an ordinary part of discovery. Learn the normal purpose before deciding whether a packet is suspicious.