A curl command has three parts: the program name (curl), zero or more options, and a target URL. Before curl ever sees them, the shell splits the line into words and removes one layer of quoting.
Quoting matters because bodies and headers contain spaces and special characters. Single quotes are literal: everything between them is passed through untouched, which is why JSON bodies are usually wrapped in single quotes. Double quotes let the shell expand variables and interpret a few backslash escapes. A backslash at the end of a line is a line continuation, joining the next line, which is how "Copy as cURL" produces readable multi-line commands.
Options come in short and long forms. Short flags are one dash and a letter (-X, -H, -d); long flags are two dashes and a word (--request, --header, --data). Short flags can be clustered: -sSL is -s -S -L. A flag that takes a value can have the value attached with no space, so -XPOST means -X POST, which trips up quick readers.
Anything that is not an option and not an option's value is the URL. curl adds https:// when the scheme is missing.