it varies by site.
a url is structured protocal://username:[email protected]:port/page/on/site?list&of&args&seperated&by&andpersan
the protocal tells how to connect, usernsme:password tells you how to login (but its horrifically insecure and no longer generally used (except username for email)) the website and domain and port (port defaults to the protocal port so it is rarely used) tell where, the path tells you what to get, and the args are just there for the website. youtube uses v= to pick which video, and t=[time] for start time, but often its just tracking data
your particular example is invalid, @ is considered reserved for user selection, so [email protected] it can work in a path, but it usually isnt.
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