Whether you use v2rayN or something else, whatever you type into the interface ends up being translated into a config.json that is handed to the core. Knowing the skeleton of that file saves a lot of blind guessing when things break.
inbounds: where traffic enters
The local listeners. On the client side this is usually one socks and one http entry — the 10808 / 10809 pair. On a server it is the vless or vmess listener instead, with its port and TLS settings attached.
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The first element of the array is the default outbound: anything not caught by a routing rule leaves through it. Besides the one pointing at your node, configs normally carry a freedom outbound (direct) and a blackhole outbound (drop), each with a tag that routing rules can reference.
routing: who goes where
Rules are evaluated top to bottom and the first match wins. That makes ordering a more common source of mistakes than the rules themselves — put "ad domains to blackhole" after "everything to proxy" and the ad rule can never fire. The usual match fields are domain, ip, port and protocol; outboundTag decides the destination.
dns and log
dns controls which side resolves hostnames. Get it wrong and you end up connected to a node with no pages loading — see DNS leaks. In log, loglevel accepts debug, info, warning, error and none. Switch to debug while you investigate and switch back afterwards, otherwise the log file grows quickly.