Some will use special syntax forms to control which actions are done and in which order. Each procedure corresponds to a script, which can be copied. If there's a call to another procedure the little man puts the arguments on the stack before calling the procedure, then waits for the next little man to finish. Any lexical local variables are handled by using special spaces on the copy of the script. N must be a nonnegative integer, not an expression that evaluates to an intenger.
Infix operators are just names for procedures.
The precedence of an operator determines the sequence of operations. The Primer gives an overview, and REF DATA gives a lot more detail. Others are derived. E.g. lists are a derived datatype, created from pairs, which are two-element records. If lists had not been in Pop-11 we could have invented them, and defined the syntax.