A computer program is a sequence of statements that execute in order, with control flow determining which statements run and when. Understanding sequence, branching, and repetition is fundamental to programming.
Trace through simple programs by hand, noting which statements execute and in what order. Use visualization tools to see control flow branches.
Every program you will ever write is built from just three kinds of control flow: sequence, selection, and iteration. Sequence is the default — the computer reads your instructions from top to bottom, executing each one before moving to the next, like following a recipe step by step. If you write three statements in a row, they run in exactly that order, one at a time. There is no parallelism, no skipping ahead. The computer is relentlessly literal: it does what you wrote, in the order you wrote it.
Selection (branching) is what lets a program make decisions. Instead of always running the same steps, the program can check a condition and choose one path or another. "If the user typed 'yes,' do this; otherwise, do that." This is where programs stop being simple scripts and start responding to the world. Without branching, every run of the program would produce identical output — useful for calculators, useless for almost everything else.
Iteration (looping) is what lets a program repeat work. Rather than writing the same instruction a thousand times, you write it once inside a loop and let the computer handle the repetition. A loop combines sequence (do these steps) with selection (should I keep going or stop?) into a single powerful structure. Together, these three constructs — do things in order, choose between alternatives, repeat until done — are sufficient to express any computation. Every complex program, from web browsers to video games, is ultimately a composition of sequences, branches, and loops.
One subtlety worth internalizing early: the order statements are *written* in your source file is not always the order they *execute*. A branch might skip an entire block. A loop might re-execute the same block dozens of times. When you are confused about what a program does, the single most effective debugging technique is to trace the execution by hand — point to each line as the computer would encounter it, track what values change, and follow the actual path through the code rather than reading it like prose.