Logo has many facilities for controlling which instructions get executed next. Taken together, these facilities are commonly called "flow control", because they control the "flow" of execution.
In the following descriptions, an "instruction list" input may be a list or a word.
If it's a word, it is parsed into list form before it is run.
RUN READWORD or
RUN READLIST work.
The former is slightly preferable because it allows for a continued line (with
~) that includes a comment (with
;) on the first line.
Pay attention to the difference between an "operation" and a "command". An operation is a procedure that outputs a value. A command is a procedure that does NOT output a value. Most procedures are either one or the other, but some are both.