A scalar is fully pinned down by one number. A vector needs that same number paired with a direction — and the same magnitude pointed a different way is a genuinely different vector.
Some quantities in engineering and physics are "done" the moment you attach a number and a unit to them — a mass of 12 kg, a temperature of 40°C, an energy of 500 J. No direction is needed or even meaningful; the quantity is completely specified by its magnitude alone. These are scalar quantities — speed, mass, temperature, energy, and distance (the total length of a path traveled) are all scalars. Other quantities aren't fully described until you also say which way they point — a force of 12 N means nothing structurally useful until you know its direction, and neither does a velocity of 20 m/s. These are vector quantities — velocity, displacement (the straight-line change in position, as opposed to distance's total path length), force, acceleration, and momentum all require magnitude anddirection to mean anything complete. Mixing up the scalar and vector versions of a related concept isn't just sloppy wording — it produces genuinely wrong answers about acceleration and net motion.